CINXE.COM

<!doctype html><html lang="en-US" prefix="og: https://ogp.me/ns#"><head><meta charSet="utf-8"/><meta name="viewport" content="width=device-width,initial-scale=1"/><link rel="icon" href="https://developer.mozilla.org/favicon-48x48.bc390275e955dacb2e65.png"/><link rel="apple-touch-icon" href="https://developer.mozilla.org/apple-touch-icon.528534bba673c38049c2.png"/><meta name="theme-color" content="#ffffff"/><link rel="manifest" href="https://developer.mozilla.org/manifest.f42880861b394dd4dc9b.json"/><link rel="search" type="application/opensearchdescription+xml" href="/opensearch.xml" title="MDN Web Docs"/><title>Capabilities, constraints, and settings - Web APIs | MDN</title><link rel="alternate" title="Fähigkeiten, Einschränkungen und Einstellungen" href="https://developer.mozilla.org/de/docs/Web/API/Media_Capture_and_Streams_API/Constraints" hrefLang="de"/><link rel="alternate" title="能力と制約と設定" href="https://developer.mozilla.org/ja/docs/Web/API/Media_Capture_and_Streams_API/Constraints" hrefLang="ja"/><link rel="alternate" title="Capabilities, constraints, and settings" href="https://developer.mozilla.org/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints" hrefLang="en"/><link rel="preload" as="font" type="font/woff2" href="/static/media/Inter.var.c2fe3cb2b7c746f7966a.woff2" crossorigin=""/><link rel="alternate" type="application/rss+xml" title="MDN Blog RSS Feed" href="https://developer.mozilla.org/en-US/blog/rss.xml" hrefLang="en"/><meta name="description" content="This article discusses the twin concepts of constraints and capabilities, as well as media settings, and includes an example we call the Constraint Exerciser. The Constraint Exerciser lets you experiment with the results of different constraint sets being applied to the audio and video tracks coming from the computer's A/V input devices (such as its webcam and microphone)."/><meta property="og:url" content="https://developer.mozilla.org/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints"/><meta property="og:title" content="Capabilities, constraints, and settings - Web APIs | MDN"/><meta property="og:type" content="website"/><meta property="og:locale" content="en_US"/><meta property="og:description" content="This article discusses the twin concepts of constraints and capabilities, as well as media settings, and includes an example we call the Constraint Exerciser. The Constraint Exerciser lets you experiment with the results of different constraint sets being applied to the audio and video tracks coming from the computer's A/V input devices (such as its webcam and microphone)."/><meta property="og:image" content="https://developer.mozilla.org/mdn-social-share.d893525a4fb5fb1f67a2.png"/><meta property="og:image:type" content="image/png"/><meta property="og:image:height" content="1080"/><meta property="og:image:width" content="1920"/><meta property="og:image:alt" content="The MDN Web Docs logo, featuring a blue accent color, displayed on a solid black background."/><meta property="og:site_name" content="MDN Web Docs"/><meta name="twitter:card" content="summary_large_image"/><meta name="twitter:creator" content="MozDevNet"/><link rel="canonical" href="https://developer.mozilla.org/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints"/><style media="print">.article-actions-container,.document-toc-container,.language-menu,.main-menu-toggle,.on-github,.page-footer,.place,.sidebar,.top-banner,.top-navigation-main,ul.prev-next{display:none!important}.main-page-content,.main-page-content pre{padding:2px}.main-page-content pre{border-left-width:2px}</style><script src="/static/js/gtag.js" defer=""></script><script defer="" src="/static/js/main.5e889624.js"></script><link href="/static/css/main.26c64ea7.css" rel="stylesheet"/></head><body><script>if(document.body.addEventListener("load",(t=>{t.target.classList.contains("interactive")&&t.target.setAttribute("data-readystate","complete")}),{capture:!0}),window&&document.documentElement){const t={light:"#ffffff",dark:"#1b1b1b"};try{const e=window.localStorage.getItem("theme");e&&(document.documentElement.className=e,document.documentElement.style.backgroundColor=t[e]);const o=window.localStorage.getItem("nop");o&&(document.documentElement.dataset.nop=o)}catch(t){console.warn("Unable to read theme from localStorage",t)}}</script><div id="root"><ul id="nav-access" class="a11y-nav"><li><a id="skip-main" href="#content">Skip to main content</a></li><li><a id="skip-search" href="#top-nav-search-input">Skip to search</a></li><li><a id="skip-select-language" href="#languages-switcher-button">Skip to select language</a></li></ul><div class="page-wrapper category-api document-page"><div class="top-banner loading"><section class="place top container"></section></div><div class="sticky-header-container"><header class="top-navigation "><div class="container "><div class="top-navigation-wrap"><a href="/en-US/" class="logo" aria-label="MDN homepage"><svg id="mdn-docs-logo" xmlns="http://www.w3.org/2000/svg" x="0" y="0" viewBox="0 0 694.9 104.4" style="enable-background:new 0 0 694.9 104.4" xml:space="preserve" role="img"><title>MDN Web Docs</title><path d="M40.3 0 11.7 92.1H0L28.5 0h11.8zm10.4 0v92.1H40.3V0h10.4zM91 0 62.5 92.1H50.8L79.3 0H91zm10.4 0v92.1H91V0h10.4z" class="logo-m"></path><path d="M627.9 95.6h67v8.8h-67v-8.8z" class="logo-_"></path><path d="M367 42h-4l-10.7 30.8h-5.5l-10.8-26h-.4l-10.5 26h-5.2L308.7 42h-3.8v-5.6H323V42h-6.5l6.8 20.4h.4l10.3-26h4.7l11.2 26h.5l5.7-20.3h-6.2v-5.6H367V42zm34.9 20c-.4 3.2-2 5.9-4.7 8.2-2.8 2.3-6.5 3.4-11.3 3.4-5.4 0-9.7-1.6-13.1-4.7-3.3-3.2-5-7.7-5-13.7 0-5.7 1.6-10.3 4.7-14s7.4-5.5 12.9-5.5c5.1 0 9.1 1.6 11.9 4.7s4.3 6.9 4.3 11.3c0 1.5-.2 3-.5 4.7h-25.6c.3 7.7 4 11.6 10.9 11.6 2.9 0 5.1-.7 6.5-2 1.5-1.4 2.5-3 3-4.9l6 .9zM394 51.3c.2-2.4-.4-4.7-1.8-6.9s-3.8-3.3-7-3.3c-3.1 0-5.3 1-6.9 3-1.5 2-2.5 4.4-2.8 7.2H394zm51 2.4c0 5-1.3 9.5-4 13.7s-6.9 6.2-12.7 6.2c-6 0-10.3-2.2-12.7-6.7-.1.4-.2 1.4-.4 2.9s-.3 2.5-.4 2.9h-7.3c.3-1.7.6-3.5.8-5.3.3-1.8.4-3.7.4-5.5V22.3h-6v-5.6H416v27c1.1-2.2 2.7-4.1 4.7-5.7 2-1.6 4.8-2.4 8.4-2.4 4.6 0 8.4 1.6 11.4 4.7 3 3.2 4.5 7.6 4.5 13.4zm-7.7.6c0-4.2-1-7.4-3-9.5-2-2.2-4.4-3.3-7.4-3.3-3.4 0-6 1.2-8 3.7-1.9 2.4-2.9 5-3 7.7V57c0 3 1 5.6 3 7.7s4.5 3.1 7.6 3.1c3.6 0 6.3-1.3 8.1-3.9 1.8-2.7 2.7-5.9 2.7-9.6zm69.2 18.5h-13.2v-7.2c-1.2 2.2-2.8 4.1-4.9 5.6-2.1 1.6-4.8 2.4-8.3 2.4-4.8 0-8.7-1.6-11.6-4.9-2.9-3.2-4.3-7.7-4.3-13.3 0-5 1.3-9.6 4-13.7 2.6-4.1 6.9-6.2 12.8-6.2 5.7 0 9.8 2.2 12.3 6.5V22.3h-8.6v-5.6h15.8v50.6h6v5.5zM493.2 56v-4.4c-.1-3-1.2-5.5-3.2-7.3s-4.4-2.8-7.2-2.8c-3.6 0-6.3 1.3-8.2 3.9-1.9 2.6-2.8 5.8-2.8 9.6 0 4.1 1 7.3 3 9.5s4.5 3.3 7.4 3.3c3.2 0 5.8-1.3 7.8-3.8 2.1-2.6 3.1-5.3 3.2-8zm53.1-1.4c0 5.6-1.8 10.2-5.3 13.7s-8.2 5.3-13.9 5.3-10.1-1.7-13.4-5.1c-3.3-3.4-5-7.9-5-13.5 0-5.3 1.6-9.9 4.7-13.7 3.2-3.8 7.9-5.7 14.2-5.7s11 1.9 14.1 5.7c3 3.7 4.6 8.1 4.6 13.3zm-7.7-.2c0-4-1-7.2-3-9.5s-4.8-3.5-8.2-3.5c-3.6 0-6.4 1.2-8.3 3.7s-2.9 5.6-2.9 9.5c0 3.7.9 6.8 2.8 9.4 1.9 2.6 4.6 3.9 8.3 3.9 3.6 0 6.4-1.3 8.4-3.8 1.9-2.6 2.9-5.8 2.9-9.7zm45 5.8c-.4 3.2-1.9 6.3-4.4 9.1-2.5 2.9-6.4 4.3-11.8 4.3-5.2 0-9.4-1.6-12.6-4.8-3.2-3.2-4.8-7.7-4.8-13.7 0-5.5 1.6-10.1 4.7-13.9 3.2-3.8 7.6-5.7 13.2-5.7 2.3 0 4.6.3 6.7.8 2.2.5 4.2 1.5 6.2 2.9l1.5 9.5-5.9.7-1.3-6.1c-2.1-1.2-4.5-1.8-7.2-1.8-3.5 0-6.1 1.2-7.7 3.7-1.7 2.5-2.5 5.7-2.5 9.6 0 4.1.9 7.3 2.7 9.5 1.8 2.3 4.4 3.4 7.8 3.4 5.2 0 8.2-2.9 9.2-8.8l6.2 1.3zm34.7 1.9c0 3.6-1.5 6.5-4.6 8.5s-7 3-11.7 3c-5.7 0-10.6-1.2-14.6-3.6l1.2-8.8 5.7.6-.2 4.7c1.1.5 2.3.9 3.6 1.1s2.6.3 3.9.3c2.4 0 4.5-.4 6.5-1.3 1.9-.9 2.9-2.2 2.9-4.1 0-1.8-.8-3.1-2.3-3.8s-3.5-1.3-5.8-1.7-4.6-.9-6.9-1.4c-2.3-.6-4.2-1.6-5.7-2.9-1.6-1.4-2.3-3.5-2.3-6.3 0-4.1 1.5-6.9 4.6-8.5s6.4-2.4 9.9-2.4c2.6 0 5 .3 7.2.9 2.2.6 4.3 1.4 6.1 2.4l.8 8.8-5.8.7-.8-5.7c-2.3-1-4.7-1.6-7.2-1.6-2.1 0-3.7.4-5.1 1.1-1.3.8-2 2-2 3.8 0 1.7.8 2.9 2.3 3.6 1.5.7 3.4 1.2 5.7 1.6 2.2.4 4.5.8 6.7 1.4 2.2.6 4.1 1.6 5.7 3 1.4 1.6 2.2 3.7 2.2 6.6zM197.6 73.2h-17.1v-5.5h3.8V51.9c0-3.7-.7-6.3-2.1-7.9-1.4-1.6-3.3-2.3-5.7-2.3-3.2 0-5.6 1.1-7.2 3.4s-2.4 4.6-2.5 6.9v15.6h6v5.5h-17.1v-5.5h3.8V51.9c0-3.8-.7-6.4-2.1-7.9-1.4-1.5-3.3-2.3-5.6-2.3-3.2 0-5.5 1.1-7.2 3.3-1.6 2.2-2.4 4.5-2.5 6.9v15.8h6.9v5.5h-20.2v-5.5h6V42.4h-6.1v-5.6h13.4v6.4c1.2-2.1 2.7-3.8 4.7-5.2 2-1.3 4.4-2 7.3-2s5.3.7 7.5 2.1c2.2 1.4 3.7 3.5 4.5 6.4 1.1-2.5 2.7-4.5 4.9-6.1s4.8-2.4 7.9-2.4c3.5 0 6.5 1.1 8.9 3.3s3.7 5.6 3.7 10.2v18.2h6.1v5.5zm42.5 0h-13.2V66c-1.2 2.2-2.8 4.1-4.9 5.6-2.1 1.6-4.8 2.4-8.3 2.4-4.8 0-8.7-1.6-11.6-4.9-2.9-3.2-4.3-7.7-4.3-13.3 0-5 1.3-9.6 4-13.7 2.6-4.1 6.9-6.2 12.8-6.2s9.8 2.2 12.3 6.5V22.7h-8.6v-5.6h15.8v50.6h6v5.5zm-13.3-16.8V52c-.1-3-1.2-5.5-3.2-7.3s-4.4-2.8-7.2-2.8c-3.6 0-6.3 1.3-8.2 3.9-1.9 2.6-2.8 5.8-2.8 9.6 0 4.1 1 7.3 3 9.5s4.5 3.3 7.4 3.3c3.2 0 5.8-1.3 7.8-3.8 2.1-2.6 3.1-5.3 3.2-8zm61.5 16.8H269v-5.5h6V51.9c0-3.7-.7-6.3-2.2-7.9-1.4-1.6-3.4-2.3-5.7-2.3-3.1 0-5.6 1-7.4 3s-2.8 4.4-2.9 7v15.9h6v5.5h-19.3v-5.5h6V42.4h-6.2v-5.6h13.6V43c2.6-4.6 6.8-6.9 12.7-6.9 3.6 0 6.7 1.1 9.2 3.3s3.7 5.6 3.7 10.2v18.2h6v5.4h-.2z" class="logo-text"></path></svg></a><button title="Open main menu" type="button" class="button action has-icon main-menu-toggle" aria-haspopup="menu" aria-label="Open main menu" aria-expanded="false"><span class="button-wrap"><span class="icon icon-menu "></span><span class="visually-hidden">Open main menu</span></span></button></div><div class="top-navigation-main"><nav class="main-nav" aria-label="Main menu"><ul class="main-menu nojs"><li class="top-level-entry-container active"><button type="button" id="references-button" class="top-level-entry menu-toggle" aria-controls="references-menu" aria-expanded="false">References</button><a href="/en-US/docs/Web" class="top-level-entry">References</a><ul id="references-menu" class="submenu references hidden inline-submenu-lg" aria-labelledby="references-button"><li class="apis-link-container mobile-only "><a href="/en-US/docs/Web" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Overview / Web Technology</div><p class="submenu-item-description">Web technology reference for developers</p></div></a></li><li class="html-link-container "><a href="/en-US/docs/Web/HTML" class="submenu-item "><div class="submenu-icon html"></div><div class="submenu-content-container"><div class="submenu-item-heading">HTML</div><p class="submenu-item-description">Structure of content on the web</p></div></a></li><li class="css-link-container "><a href="/en-US/docs/Web/CSS" class="submenu-item "><div class="submenu-icon css"></div><div class="submenu-content-container"><div class="submenu-item-heading">CSS</div><p class="submenu-item-description">Code used to describe document style</p></div></a></li><li class="javascript-link-container "><a href="/en-US/docs/Web/JavaScript" class="submenu-item "><div class="submenu-icon javascript"></div><div class="submenu-content-container"><div class="submenu-item-heading">JavaScript</div><p class="submenu-item-description">General-purpose scripting language</p></div></a></li><li class="http-link-container "><a href="/en-US/docs/Web/HTTP" class="submenu-item "><div class="submenu-icon http"></div><div class="submenu-content-container"><div class="submenu-item-heading">HTTP</div><p class="submenu-item-description">Protocol for transmitting web resources</p></div></a></li><li class="apis-link-container "><a href="/en-US/docs/Web/API" class="submenu-item "><div class="submenu-icon apis"></div><div class="submenu-content-container"><div class="submenu-item-heading">Web APIs</div><p class="submenu-item-description">Interfaces for building web applications</p></div></a></li><li class="apis-link-container "><a href="/en-US/docs/Mozilla/Add-ons/WebExtensions" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Web Extensions</div><p class="submenu-item-description">Developing extensions for web browsers</p></div></a></li><li class="apis-link-container desktop-only "><a href="/en-US/docs/Web" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Web Technology</div><p class="submenu-item-description">Web technology reference for developers</p></div></a></li></ul></li><li class="top-level-entry-container "><button type="button" id="guides-button" class="top-level-entry menu-toggle" aria-controls="guides-menu" aria-expanded="false">Guides</button><a href="/en-US/docs/Learn" class="top-level-entry">Guides</a><ul id="guides-menu" class="submenu guides hidden inline-submenu-lg" aria-labelledby="guides-button"><li class="apis-link-container mobile-only "><a href="/en-US/docs/Learn" class="submenu-item "><div class="submenu-icon learn"></div><div class="submenu-content-container"><div class="submenu-item-heading">Overview / MDN Learning Area</div><p class="submenu-item-description">Learn web development</p></div></a></li><li class="apis-link-container desktop-only "><a href="/en-US/docs/Learn" class="submenu-item "><div class="submenu-icon learn"></div><div class="submenu-content-container"><div class="submenu-item-heading">MDN Learning Area</div><p class="submenu-item-description">Learn web development</p></div></a></li><li class="html-link-container "><a href="/en-US/docs/Learn/HTML" class="submenu-item "><div class="submenu-icon html"></div><div class="submenu-content-container"><div class="submenu-item-heading">HTML</div><p class="submenu-item-description">Learn to structure web content with HTML</p></div></a></li><li class="css-link-container "><a href="/en-US/docs/Learn/CSS" class="submenu-item "><div class="submenu-icon css"></div><div class="submenu-content-container"><div class="submenu-item-heading">CSS</div><p class="submenu-item-description">Learn to style content using CSS</p></div></a></li><li class="javascript-link-container "><a href="/en-US/docs/Learn/JavaScript" class="submenu-item "><div class="submenu-icon javascript"></div><div class="submenu-content-container"><div class="submenu-item-heading">JavaScript</div><p class="submenu-item-description">Learn to run scripts in the browser</p></div></a></li><li class=" "><a href="/en-US/docs/Web/Accessibility" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Accessibility</div><p class="submenu-item-description">Learn to make the web accessible to all</p></div></a></li></ul></li><li class="top-level-entry-container "><button type="button" id="mdn-plus-button" class="top-level-entry menu-toggle" aria-controls="mdn-plus-menu" aria-expanded="false">Plus</button><a href="/en-US/plus" class="top-level-entry">Plus</a><ul id="mdn-plus-menu" class="submenu mdn-plus hidden inline-submenu-lg" aria-labelledby="mdn-plus-button"><li class=" "><a href="/en-US/plus" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Overview</div><p class="submenu-item-description">A customized MDN experience</p></div></a></li><li class=" "><a href="/en-US/plus/ai-help" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">AI Help</div><p class="submenu-item-description">Get real-time assistance and support</p></div></a></li><li class=" "><a href="/en-US/plus/updates" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Updates</div><p class="submenu-item-description">All browser compatibility updates at a glance</p></div></a></li><li class=" "><a href="/en-US/plus/docs/features/overview" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Documentation</div><p class="submenu-item-description">Learn how to use MDN Plus</p></div></a></li><li class=" "><a href="/en-US/plus/docs/faq" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">FAQ</div><p class="submenu-item-description">Frequently asked questions about MDN Plus</p></div></a></li></ul></li><li class="top-level-entry-container "><a class="top-level-entry menu-link" href="/en-US/curriculum/">Curriculum <sup class="new">New</sup></a></li><li class="top-level-entry-container "><a class="top-level-entry menu-link" href="/en-US/blog/">Blog</a></li><li class="top-level-entry-container "><button type="button" id="tools-button" class="top-level-entry menu-toggle" aria-controls="tools-menu" aria-expanded="false">Tools</button><ul id="tools-menu" class="submenu tools hidden inline-submenu-lg" aria-labelledby="tools-button"><li class=" "><a href="/en-US/play" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">Playground</div><p class="submenu-item-description">Write, test and share your code</p></div></a></li><li class=" "><a href="/en-US/observatory" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">HTTP Observatory</div><p class="submenu-item-description">Scan a website for free</p></div></a></li><li class=" "><a href="/en-US/plus/ai-help" class="submenu-item "><div class="submenu-icon"></div><div class="submenu-content-container"><div class="submenu-item-heading">AI Help</div><p class="submenu-item-description">Get real-time assistance and support</p></div></a></li></ul></li></ul></nav><div class="header-search"><form action="/en-US/search" class="search-form search-widget" id="top-nav-search-form" role="search"><label id="top-nav-search-label" for="top-nav-search-input" class="visually-hidden">Search MDN</label><input aria-activedescendant="" aria-autocomplete="list" aria-controls="top-nav-search-menu" aria-expanded="false" aria-labelledby="top-nav-search-label" autoComplete="off" id="top-nav-search-input" role="combobox" type="search" class="search-input-field" name="q" placeholder=" " required="" value=""/><button type="button" class="button action has-icon clear-search-button"><span class="button-wrap"><span class="icon icon-cancel "></span><span class="visually-hidden">Clear search input</span></span></button><button type="submit" class="button action has-icon search-button"><span class="button-wrap"><span class="icon icon-search "></span><span class="visually-hidden">Search</span></span></button><div id="top-nav-search-menu" role="listbox" aria-labelledby="top-nav-search-label"></div></form></div><div class="theme-switcher-menu"><button type="button" class="button action has-icon theme-switcher-menu small" aria-haspopup="menu"><span class="button-wrap"><span class="icon icon-theme-os-default "></span>Theme</span></button></div><ul class="auth-container"><li><a href="/users/fxa/login/authenticate/?next=%2Fen-US%2Fdocs%2FWeb%2FAPI%2FMedia_Capture_and_Streams_API%2FConstraints" class="login-link" rel="nofollow">Log in</a></li><li><a href="/users/fxa/login/authenticate/?next=%2Fen-US%2Fdocs%2FWeb%2FAPI%2FMedia_Capture_and_Streams_API%2FConstraints" target="_self" rel="nofollow" class="button primary mdn-plus-subscribe-link"><span class="button-wrap">Sign up for free</span></a></li></ul></div></div></header><div class="article-actions-container"><div class="container"><button type="button" class="button action has-icon sidebar-button" aria-label="Expand sidebar" aria-expanded="false" aria-controls="sidebar-quicklinks"><span class="button-wrap"><span class="icon icon-sidebar "></span></span></button><nav class="breadcrumbs-container" aria-label="Breadcrumb"><ol typeof="BreadcrumbList" vocab="https://schema.org/" aria-label="breadcrumbs"><li property="itemListElement" typeof="ListItem"><a href="/en-US/docs/Web" class="breadcrumb" property="item" typeof="WebPage"><span property="name">References</span></a><meta property="position" content="1"/></li><li property="itemListElement" typeof="ListItem"><a href="/en-US/docs/Web/API" class="breadcrumb" property="item" typeof="WebPage"><span property="name">Web APIs</span></a><meta property="position" content="2"/></li><li property="itemListElement" typeof="ListItem"><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API" class="breadcrumb" property="item" typeof="WebPage"><span property="name">Media Capture and Streams API (Media Stream)</span></a><meta property="position" content="3"/></li><li property="itemListElement" typeof="ListItem"><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints" class="breadcrumb-current-page" property="item" typeof="WebPage"><span property="name">Capabilities, constraints, and settings</span></a><meta property="position" content="4"/></li></ol></nav><div class="article-actions"><button type="button" class="button action has-icon article-actions-toggle" aria-label="Article actions"><span class="button-wrap"><span class="icon icon-ellipses "></span><span class="article-actions-dialog-heading">Article Actions</span></span></button><ul class="article-actions-entries"><li class="article-actions-entry"><div class="languages-switcher-menu open-on-focus-within"><button id="languages-switcher-button" type="button" class="button action small has-icon languages-switcher-menu" aria-haspopup="menu"><span class="button-wrap"><span class="icon icon-language "></span>English (US)</span></button><div class="hidden"><ul class="submenu language-menu " aria-labelledby="language-menu-button"><li class=" "><form class="submenu-item locale-redirect-setting"><div class="group"><label class="switch"><input type="checkbox" name="locale-redirect"/><span class="slider"></span><span class="label">Remember language</span></label><a href="https://github.com/orgs/mdn/discussions/739" rel="external noopener noreferrer" target="_blank" title="Enable this setting to automatically switch to this language when it's available. (Click to learn more.)"><span class="icon icon-question-mark "></span></a></div></form></li><li class=" "><a data-locale="de" href="/de/docs/Web/API/Media_Capture_and_Streams_API/Constraints" class="button submenu-item"><span>Deutsch</span><span title="Diese Übersetzung ist Teil eines Experiments."><span class="icon icon-experimental "></span></span></a></li><li class=" "><a data-locale="ja" href="/ja/docs/Web/API/Media_Capture_and_Streams_API/Constraints" class="button submenu-item"><span>日本語</span></a></li></ul></div></div></li></ul></div></div></div></div><div class="main-wrapper"><div class="sidebar-container"><aside id="sidebar-quicklinks" class="sidebar" data-macro="DefaultAPISidebar"><button type="button" class="button action backdrop" aria-label="Collapse sidebar"><span class="button-wrap"></span></button><nav aria-label="Related Topics" class="sidebar-inner"><header class="sidebar-actions"><section class="sidebar-filter-container"><div class="sidebar-filter "><label id="sidebar-filter-label" class="sidebar-filter-label" for="sidebar-filter-input"><span class="icon icon-filter"></span><span class="visually-hidden">Filter sidebar</span></label><input id="sidebar-filter-input" autoComplete="off" class="sidebar-filter-input-field false" type="text" placeholder="Filter" value=""/><button type="button" class="button action has-icon clear-sidebar-filter-button"><span class="button-wrap"><span class="icon icon-cancel "></span><span class="visually-hidden">Clear filter input</span></span></button></div></section></header><div class="sidebar-inner-nav"><div class="in-nav-toc"><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#overview">Overview</a></li><li class="document-toc-item "><a class="document-toc-link" href="#determining_if_a_constraint_is_supported">Determining if a constraint is supported</a></li><li class="document-toc-item "><a class="document-toc-link" href="#how_constraints_are_defined">How constraints are defined</a></li><li class="document-toc-item "><a class="document-toc-link" href="#checking_capabilities">Checking capabilities</a></li><li class="document-toc-item "><a class="document-toc-link" href="#applying_constraints">Applying constraints</a></li><li class="document-toc-item "><a class="document-toc-link" href="#retrieving_current_constraints_and_settings">Retrieving current constraints and settings</a></li><li class="document-toc-item "><a class="document-toc-link" href="#example_constraint_exerciser">Example: Constraint exerciser</a></li><li class="document-toc-item "><a class="document-toc-link" href="#specifications">Specifications</a></li><li class="document-toc-item "><a class="document-toc-link" href="#browser_compatibility">Browser compatibility</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></div><div class="sidebar-body"><ol><li class="section"><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API">Media Capture and Streams API</a></li><li class="toggle"><details open=""><summary>Guides</summary><ol><li><em><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints" aria-current="page">Capabilities, constraints, and settings</a></em></li><li><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API/Taking_still_photos">Taking still photos with getUserMedia()</a></li></ol></details></li><li class="toggle"><details open=""><summary>Interfaces</summary><ol><li><a href="/en-US/docs/Web/API/CanvasCaptureMediaStreamTrack"><code>CanvasCaptureMediaStreamTrack</code></a></li><li><a href="/en-US/docs/Web/API/InputDeviceInfo"><code>InputDeviceInfo</code></a></li><li><a href="/en-US/docs/Web/API/MediaDeviceInfo"><code>MediaDeviceInfo</code></a></li><li><a href="/en-US/docs/Web/API/MediaDevices"><code>MediaDevices</code></a></li><li><a href="/en-US/docs/Web/API/MediaStream"><code>MediaStream</code></a></li><li><a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a></li><li><a href="/en-US/docs/Web/API/MediaStreamTrackEvent"><code>MediaStreamTrackEvent</code></a></li><li><a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a></li><li><a href="/en-US/docs/Web/API/MediaTrackSettings"><code>MediaTrackSettings</code></a></li><li><a href="/en-US/docs/Web/API/MediaTrackSupportedConstraints"><code>MediaTrackSupportedConstraints</code></a></li><li><a href="/en-US/docs/Web/API/OverconstrainedError"><code>OverconstrainedError</code></a></li></ol></details></li><li class="toggle"><details open=""><summary>Properties</summary><ol><li><a href="/en-US/docs/Web/API/Navigator/mediaDevices"><code>Navigator.mediaDevices</code></a></li></ol></details></li><li class="toggle"><details open=""><summary>Methods</summary><ol><li><a href="/en-US/docs/Web/API/HTMLCanvasElement/captureStream"><code>HTMLCanvasElement.captureStream()</code></a></li><li><a href="/en-US/docs/Web/API/HTMLMediaElement/captureStream"><code>HTMLMediaElement.captureStream()</code></a></li></ol></details></li></ol></div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#overview">Overview</a></li><li class="document-toc-item "><a class="document-toc-link" href="#determining_if_a_constraint_is_supported">Determining if a constraint is supported</a></li><li class="document-toc-item "><a class="document-toc-link" href="#how_constraints_are_defined">How constraints are defined</a></li><li class="document-toc-item "><a class="document-toc-link" href="#checking_capabilities">Checking capabilities</a></li><li class="document-toc-item "><a class="document-toc-link" href="#applying_constraints">Applying constraints</a></li><li class="document-toc-item "><a class="document-toc-link" href="#retrieving_current_constraints_and_settings">Retrieving current constraints and settings</a></li><li class="document-toc-item "><a class="document-toc-link" href="#example_constraint_exerciser">Example: Constraint exerciser</a></li><li class="document-toc-item "><a class="document-toc-link" href="#specifications">Specifications</a></li><li class="document-toc-item "><a class="document-toc-link" href="#browser_compatibility">Browser compatibility</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>Capabilities, constraints, and settings</h1></header><div class="section-content"><p>This article discusses the twin concepts of <strong>constraints</strong> and <strong>capabilities</strong>, as well as media settings, and includes an example we call the <a href="#example_constraint_exerciser">Constraint Exerciser</a>. The Constraint Exerciser lets you experiment with the results of different constraint sets being applied to the audio and video tracks coming from the computer's A/V input devices (such as its webcam and microphone).</p> <p>Historically, writing scripts for the Web that work intimately with Web APIs has had a well-known challenge: often, your code needs to know whether or not an API exists and if so, what its limitations are on the <a href="/en-US/docs/Glossary/User_agent">user agent</a> it's running on. Figuring this out has often been difficult, and has usually involved looking at some combination of which <a href="/en-US/docs/Glossary/User_agent">user agent</a> (or browser) you're running on, which version it is, looking to see if certain objects exist, trying to see whether various things work or not and determining what errors occur, and so forth. The result has been a lot of very fragile code, or a reliance on libraries which figure this stuff out for you, then implement <a href="/en-US/docs/Glossary/Polyfill">polyfills</a> to patch the holes in the implementation on your behalf.</p> <p>Capabilities and constraints let the browser and website or app exchange information about what <strong>constrainable properties</strong> the browser's implementation supports and what values it supports for each.</p></div><section aria-labelledby="overview"><h2 id="overview"><a href="#overview">Overview</a></h2><div class="section-content"><p>The process works like this (using <a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a> as an example):</p> <ol> <li>If needed, call <a href="/en-US/docs/Web/API/MediaDevices/getSupportedConstraints"><code>MediaDevices.getSupportedConstraints()</code></a> to get the list of <strong>supported constraints</strong>, which tells you what constrainable properties the browser knows about. This isn't always necessary, since any that aren't known will be ignored when you specify them—but if you have any that you can't get by without, you can start by checking to be sure they're on the list.</li> <li>Once the script knows whether the property or properties it wishes to use are supported, it can then check the <strong>capabilities</strong> of the API and its implementation by examining the object returned by the track's <code>getCapabilities()</code> method; this object lists each supported constraint and the values or range of values which are supported.</li> <li>Finally, the track's <code>applyConstraints()</code> method is called to configure the API as desired by specifying the values or ranges of values it wishes to use for any of the constrainable properties about which it has a preference.</li> <li>The track's <code>getConstraints()</code> method returns the set of constraints passed into the most recent call to <code>applyConstraints()</code>. This may not represent the actual current state of the track, due to properties whose requested values had to be adjusted and because platform default values aren't represented. For a complete representation of the track's current configuration, use <code>getSettings()</code>.</li> </ol> <p>In the Media Capture and Streams API, both <a href="/en-US/docs/Web/API/MediaStream"><code>MediaStream</code></a> and <a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a> have constrainable properties.</p></div></section><section aria-labelledby="determining_if_a_constraint_is_supported"><h2 id="determining_if_a_constraint_is_supported"><a href="#determining_if_a_constraint_is_supported">Determining if a constraint is supported</a></h2><div class="section-content"><p>If you need to know whether or not a given constraint is supported by the user agent, you can find out by calling <a href="/en-US/docs/Web/API/MediaDevices/getSupportedConstraints" title="navigator.mediaDevices.getSupportedConstraints()"><code>navigator.mediaDevices.getSupportedConstraints()</code></a> to get a list of the constrainable properties which the browser knows, like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const supported = navigator.mediaDevices.getSupportedConstraints(); document.getElementById("frameRateSlider").disabled = !supported["frameRate"]; </code></pre></div> <p>In this example, the supported constraints are fetched, and a control that lets the user configure the frame rate is disabled if the <code>frameRate</code> constraint isn't supported.</p></div></section><section aria-labelledby="how_constraints_are_defined"><h2 id="how_constraints_are_defined"><a href="#how_constraints_are_defined">How constraints are defined</a></h2><div class="section-content"><p>A single constraint is an object whose name matches the constrainable property whose desired value or range of values is being specified. This object contains zero or more individual constraints, as well as an optional sub-object named <code>advanced</code>, which contains another set of zero or more constraints which the user agent must satisfy if at all possible. The user agent attempts to satisfy constraints in the order specified in the constraint set.</p> <p>The most important thing to understand is that most constraints aren't requirements; instead, they're requests. There are exceptions, and we'll get to those shortly.</p></div></section><section aria-labelledby="requesting_a_specific_value_for_a_setting"><h3 id="requesting_a_specific_value_for_a_setting"><a href="#requesting_a_specific_value_for_a_setting">Requesting a specific value for a setting</a></h3><div class="section-content"><p>Most, each constraint may be a specific value indicating a desired value for the setting. For example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const constraints = { width: 1920, height: 1080, aspectRatio: 1.777777778, }; myTrack.applyConstraints(constraints); </code></pre></div> <p>In this case, the constraints indicate that any values are fine for nearly all properties, but that a standard high definition (HD) video size is desired, with the standard 16:9 <a href="/en-US/docs/Glossary/Aspect_ratio">aspect ratio</a>. There's no guarantee that the resulting track will match any of these, but the user agent should do its best to match as many as possible.</p> <p>The prioritization of the properties is simple: if two properties' requested values are mutually exclusive, then the one listed first in the constraint set will be used. As an example, if the browser running the code above couldn't provide a 1920x1080 track but could do 1920x900, then that's what would be provided.</p> <p>Simple constraints like these, specifying a single value, are always treated as non-required. The user agent will try to provide what you request but will not guarantee that what you get will match. However, if you use simple values for properties when calling <a href="/en-US/docs/Web/API/MediaStreamTrack/applyConstraints"><code>MediaStreamTrack.applyConstraints()</code></a>, the request will always succeed, because these values will be considered a request, not a requirement.</p></div></section><section aria-labelledby="specifying_a_range_of_values"><h3 id="specifying_a_range_of_values"><a href="#specifying_a_range_of_values">Specifying a range of values</a></h3><div class="section-content"><p>Sometimes, any value within a range is acceptable for a property's value. You can specify ranges with either or both minimum and maximum values, and you can even specify an ideal value within the range, if you choose. If you provide an ideal value, the browser will try to get as close as possible to matching that value, given the other constraints specified.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const supports = navigator.mediaDevices.getSupportedConstraints(); if ( !supports["width"] || !supports["height"] || !supports["frameRate"] || !supports["facingMode"] ) { // We're missing needed properties, so handle that error. } else { const constraints = { width: { min: 640, ideal: 1920, max: 1920 }, height: { min: 400, ideal: 1080 }, aspectRatio: 1.777777778, frameRate: { max: 30 }, facingMode: { exact: "user" }, }; myTrack .applyConstraints(constraints) .then(() => { /* do stuff if constraints applied successfully */ }) .catch((reason) => { /* failed to apply constraints; reason is why */ }); } </code></pre></div> <p>Here, after ensuring that the constrainable properties for which matches must be found are supported (<code>width</code>, <code>height</code>, <code>frameRate</code>, and <code>facingMode</code>), we set up constraints which request a width no smaller than 640 and no larger than 1920 (but preferably 1920), a height no smaller than 400 (but ideally 1080), an aspect ratio of 16:9 (1.777777778), and a frame rate no greater than 30 frames per second. In addition, the only acceptable input device is a camera facing the user (a "selfie cam"). If the <code>width</code>, <code>height</code>, <code>frameRate</code>, or <code>facingMode</code> constraints can't be met, the promise returned by <code>applyConstraints()</code> will be rejected.</p> <div class="notecard note"> <p><strong>Note:</strong> Constraints which are specified using any or all of <code>max</code>, <code>min</code>, or <code>exact</code> are always treated as mandatory. If any constraint which uses one or more of those can't be met when calling <code>applyConstraints()</code>, the promise will be rejected.</p> </div></div></section><section aria-labelledby="advanced_constraints"><h3 id="advanced_constraints"><a href="#advanced_constraints">Advanced constraints</a></h3><div class="section-content"><p>So-called advanced constraints are created by adding an <code>advanced</code> property to the constraint set; this property's value is an array of additional constraint sets which are considered optional. There are few if any use cases for this feature, and there is some interest in removing it from the specification, so it will not be discussed here. If you wish to learn more, see <a href="https://www.w3.org/TR/mediacapture-streams/#idl-def-Constraints" class="external" target="_blank">section 11 of the Media Capture and Streams specification</a>, past example 2.</p></div></section><section aria-labelledby="checking_capabilities"><h2 id="checking_capabilities"><a href="#checking_capabilities">Checking capabilities</a></h2><div class="section-content"><p>You can call <a href="/en-US/docs/Web/API/MediaStreamTrack/getCapabilities"><code>MediaStreamTrack.getCapabilities()</code></a> to get a list of all of the supported capabilities and the values or ranges of values which each one accepts on the current platform and user agent. This function returns an object which lists each constrainable property supported by the browser and a value or range of values which are supported for each one of those properties.</p> <p>For example, the following snippet will result in the user being asked for permission to access their local camera and microphone. Once permission is granted, <code>MediaTrackCapabilities</code> objects will be logged to the console that detail the capabilities of each <a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>navigator.mediaDevices .getUserMedia({ video: true, audio: true }) .then((stream) => { const tracks = stream.getTracks(); tracks.map((t) => console.log(t.getCapabilities())); }); </code></pre></div> <p>An example capabilities object looks like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>{ "autoGainControl": [ true, false ], "channelCount": { "max": 1, "min": 1 }, "deviceId": "jjxEMqxIhGdryqbTjDrXPWrkjy55Vte70kWpMe3Lge8=", "echoCancellation": [ true, false ], "groupId": "o2tZiEj4MwOdG/LW3HwkjpLm1D8URat4C5kt742xrVQ=", "noiseSuppression": [ true, false ] } </code></pre></div> <p>The exact contents of the object will depend on the browser and media hardware.</p></div></section><section aria-labelledby="applying_constraints"><h2 id="applying_constraints"><a href="#applying_constraints">Applying constraints</a></h2><div class="section-content"><p>The first and most common way to use constraints is to specify them when you call <a href="/en-US/docs/Web/API/MediaDevices/getUserMedia" title="getUserMedia()"><code>getUserMedia()</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>navigator.mediaDevices .getUserMedia({ video: { width: { min: 640, ideal: 1920 }, height: { min: 400, ideal: 1080 }, aspectRatio: { ideal: 1.7777777778 }, }, audio: { sampleSize: 16, channelCount: 2, }, }) .then((stream) => { videoElement.srcObject = stream; }) .catch(handleError); </code></pre></div> <p>In this example, constraints are applied at <code>getUserMedia()</code> time, asking for an ideal set of options with fallbacks for the video.</p> <div class="notecard note"> <p><strong>Note:</strong> You can specify one or more media input device IDs to establish restrictions on which input sources are allowed. To collect a list of the available devices, you can call <a href="/en-US/docs/Web/API/MediaDevices/enumerateDevices" title="navigator.mediaDevices.enumerateDevices()"><code>navigator.mediaDevices.enumerateDevices()</code></a>, then for each device which meets the desired criteria, add its <code>deviceId</code> to the <code>MediaConstraints</code> object that eventually gets passed into <code>getUserMedia()</code>.</p> </div> <p>You can also change the constraints of an existing <a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a> on the fly, by calling the track's <a href="/en-US/docs/Web/API/MediaStreamTrack/applyConstraints" title="applyConstraints()"><code>applyConstraints()</code></a> method, passing into it an object representing the constraints you wish to apply to the track:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>videoTrack.applyConstraints({ width: 1920, height: 1080, }); </code></pre></div> <p>In this snippet, the video track referenced by <code>videoTrack</code> is updated so that its resolution as closely as possible matches 1920x1080 pixels (1080p high definition).</p></div></section><section aria-labelledby="retrieving_current_constraints_and_settings"><h2 id="retrieving_current_constraints_and_settings"><a href="#retrieving_current_constraints_and_settings">Retrieving current constraints and settings</a></h2><div class="section-content"><p>It's important to remember the difference between <strong>constraints</strong> and <strong>settings</strong>. Constraints are a way to specify what values you need, want, and are willing to accept for the various constrainable properties (as described in the documentation for <a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a>), while settings are the actual values of each constrainable property at the current time.</p></div></section><section aria-labelledby="getting_the_constraints_in_effect"><h3 id="getting_the_constraints_in_effect"><a href="#getting_the_constraints_in_effect">Getting the constraints in effect</a></h3><div class="section-content"><p>If at any time you need to fetch the set of constraints that are currently applied to the media, you can get that information by calling <a href="/en-US/docs/Web/API/MediaStreamTrack/getConstraints"><code>MediaStreamTrack.getConstraints()</code></a>, as shown in the example below.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function switchCameras(track, camera) { const constraints = track.getConstraints(); constraints.facingMode = camera; track.applyConstraints(constraints); } </code></pre></div> <p>This function accepts a <a href="/en-US/docs/Web/API/MediaStreamTrack"><code>MediaStreamTrack</code></a> and a string indicating the camera facing mode to use, fetches the current constraints, sets the value of the <a href="/en-US/docs/Web/API/MediaTrackConstraints/facingMode"><code>MediaTrackConstraints.facingMode</code></a> to the specified value, then applies the updated constraint set.</p></div></section><section aria-labelledby="getting_the_current_settings_for_a_track"><h3 id="getting_the_current_settings_for_a_track"><a href="#getting_the_current_settings_for_a_track">Getting the current settings for a track</a></h3><div class="section-content"><p>Unless you only use exact constraints (which is pretty restrictive, so be sure you mean it!), there's no guarantee exactly what you're going to actually get after the constraints are applied. The values of the constrainable properties as they actually are in the resulting media are referred to as the settings. If you need to know the true format and other properties of the media, you can obtain those settings by calling <a href="/en-US/docs/Web/API/MediaStreamTrack/getSettings"><code>MediaStreamTrack.getSettings()</code></a>. This returns an object based on the dictionary <a href="/en-US/docs/Web/API/MediaTrackSettings"><code>MediaTrackSettings</code></a>. For example:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function whichCamera(track) { return track.getSettings().facingMode; } </code></pre></div> <p>This function uses <code>getSettings()</code> to obtain the track's currently in-use values for the constrainable properties and returns the value of <a href="/en-US/docs/Web/API/MediaTrackSettings/facingMode" title="facingMode"><code>facingMode</code></a>.</p></div></section><section aria-labelledby="example_constraint_exerciser"><h2 id="example_constraint_exerciser"><a href="#example_constraint_exerciser">Example: Constraint exerciser</a></h2><div class="section-content"><p>In this example, we create an exerciser which lets you experiment with media constraints by editing the source code describing the constraint sets for audio and video tracks. You can then apply those changes and see the result, including both what the stream looks like and what the actual media settings are set to after applying the new constraints.</p> <p>The HTML and CSS for this example are pretty simple, and aren't shown here. You can look at the complete example by <a href="#livesample_fullscreen=example_constraint_exerciser">clicking here</a>.</p> <div class="code-example"><pre class="brush: html hidden notranslate"><code><p> Experiment with media constraints! Edit the constraint sets for the video and audio tracks in the edit boxes on the left, then click the "Apply Constraints" button to try them out. The actual settings the browser selected and is using are shown in the boxes on the right. Below all of that, you'll see the video itself. </p> <p>Click the "Start" button to begin.</p> <h3>Constrainable properties available:</h3> <ul id="supportedConstraints"></ul> <div id="startButton" class="button">Start</div> <div class="wrapper"> <div class="track-row"> <div class="left-side"> <h3>Requested video constraints:</h3> <textarea id="videoConstraintEditor" cols="32" rows="8"></textarea> </div> <div class="right-side"> <h3>Actual video settings:</h3> <textarea id="videoSettingsText" cols="32" rows="8" disabled></textarea> </div> </div> <div class="track-row"> <div class="left-side"> <h3>Requested audio constraints:</h3> <textarea id="audioConstraintEditor" cols="32" rows="8"></textarea> </div> <div class="right-side"> <h3>Actual audio settings:</h3> <textarea id="audioSettingsText" cols="32" rows="8" disabled></textarea> </div> </div> <div class="button" id="applyButton">Apply Constraints</div> </div> <video id="video" autoplay></video> <div class="button" id="stopButton">Stop Video</div> <div id="log"></div> </code></pre></div> <div class="code-example"><pre class="brush: css hidden notranslate"><code>body { font: 14px "Open Sans", "Arial", sans-serif; } video { margin-top: 20px; border: 1px solid black; } .button { cursor: pointer; width: 150px; border: 1px solid black; font-size: 16px; text-align: center; padding-top: 2px; padding-bottom: 4px; color: white; background-color: darkgreen; } .wrapper { margin-bottom: 10px; width: 600px; } .track-row { height: 200px; } .left-side { float: left; width: calc(calc(100% / 2) - 10px); } .right-side { float: right; width: calc(calc(100% / 2) - 10px); } textarea { padding: 8px; } h3 { margin-bottom: 3px; } #supportedConstraints { column-count: 2; } #log { padding-top: 10px; } </code></pre></div></div></section><section aria-labelledby="defaults_and_variables"><h3 id="defaults_and_variables"><a href="#defaults_and_variables">Defaults and variables</a></h3><div class="section-content"><p>First we have the default constraint sets, as strings. These strings are presented in editable <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a>s, but this is the initial configuration of the stream.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const videoDefaultConstraintString = '{\n "width": 320,\n "height": 240,\n "frameRate": 30\n}'; const audioDefaultConstraintString = '{\n "sampleSize": 16,\n "channelCount": 2,\n "echoCancellation": false\n}'; </code></pre></div> <p>These defaults ask for a pretty common camera configuration, but don't insist on any property being of special importance. The browser should do its best to match these settings but will settle for anything it considers a close match.</p> <p>Then we initialize the variables which will hold the <a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a> objects for the video and audio tracks, as well as the variables which will hold references to the video and audio tracks themselves, to <code>null</code>.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>let videoConstraints = null; let audioConstraints = null; let audioTrack = null; let videoTrack = null; </code></pre></div> <p>And we get references to all of the elements we'll need to access.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const videoElement = document.getElementById("video"); const logElement = document.getElementById("log"); const supportedConstraintList = document.getElementById("supportedConstraints"); const videoConstraintEditor = document.getElementById("videoConstraintEditor"); const audioConstraintEditor = document.getElementById("audioConstraintEditor"); const videoSettingsText = document.getElementById("videoSettingsText"); const audioSettingsText = document.getElementById("audioSettingsText"); </code></pre></div> <p>These elements are:</p> <dl> <dt id="videoelement"><a href="#videoelement"><code>videoElement</code></a></dt> <dd> <p>The <a href="/en-US/docs/Web/HTML/Element/video"><code><video></code></a> element that will show the stream.</p> </dd> <dt id="logelement"><a href="#logelement"><code>logElement</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/div"><code><div></code></a> into which any error messages or other log-type output will be written.</p> </dd> <dt id="supportedconstraintlist"><a href="#supportedconstraintlist"><code>supportedConstraintList</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/ul"><code><ul></code></a> (unordered list) into which we programmatically add the names of each of the constrainable properties supported by the user's browser.</p> </dd> <dt id="videoconstrainteditor"><a href="#videoconstrainteditor"><code>videoConstraintEditor</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a> element that lets the user edit the code for the video track's constraint set.</p> </dd> <dt id="audioconstrainteditor"><a href="#audioconstrainteditor"><code>audioConstraintEditor</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a> element that lets the user edit the code for the audio track's constraint set.</p> </dd> <dt id="videosettingstext"><a href="#videosettingstext"><code>videoSettingsText</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a> (which is always disabled) that displays the current settings for the video track's constrainable properties.</p> </dd> <dt id="audiosettingstext"><a href="#audiosettingstext"><code>audioSettingsText</code></a></dt> <dd> <p>A <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a> (which is always disabled) that displays the current settings for the audio track's constrainable properties.</p> </dd> </dl> <p>Finally, we set the current contents of the two constraint set editor elements to the defaults.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>videoConstraintEditor.value = videoDefaultConstraintString; audioConstraintEditor.value = audioDefaultConstraintString; </code></pre></div></div></section><section aria-labelledby="updating_the_settings_display"><h3 id="updating_the_settings_display"><a href="#updating_the_settings_display">Updating the settings display</a></h3><div class="section-content"><p>To the right of each of the constraint set editors is a second text box which we use to display the current configuration of the track's configurable properties. This display is updated by the function <code>getCurrentSettings()</code>, which gets the current settings for the audio and video tracks and inserts the corresponding code into the tracks' settings display boxes by setting their <a href="/en-US/docs/Web/API/HTMLTextAreaElement/value"><code>value</code></a>.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function getCurrentSettings() { if (videoTrack) { videoSettingsText.value = JSON.stringify(videoTrack.getSettings(), null, 2); } if (audioTrack) { audioSettingsText.value = JSON.stringify(audioTrack.getSettings(), null, 2); } } </code></pre></div> <p>This gets called after the stream first starts up, as well as any time we've applied updated constraints, as you'll see below.</p></div></section><section aria-labelledby="building_the_track_constraint_set_objects"><h3 id="building_the_track_constraint_set_objects"><a href="#building_the_track_constraint_set_objects">Building the track constraint set objects</a></h3><div class="section-content"><p>The <code>buildConstraints()</code> function builds the <a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a> objects for the audio and video tracks using the code in the two tracks' constraint set edit boxes.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function buildConstraints() { try { videoConstraints = JSON.parse(videoConstraintEditor.value); audioConstraints = JSON.parse(audioConstraintEditor.value); } catch (error) { handleError(error); } } </code></pre></div> <p>This uses <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse"><code>JSON.parse()</code></a> to parse the code in each editor into an object. If either call to JSON.parse() throws an exception, <code>handleError()</code> is called to output the error message to the log.</p></div></section><section aria-labelledby="configuring_and_starting_the_stream"><h3 id="configuring_and_starting_the_stream"><a href="#configuring_and_starting_the_stream">Configuring and starting the stream</a></h3><div class="section-content"><p>The <code>startVideo()</code> method handles setting up and starting the video stream.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function startVideo() { buildConstraints(); navigator.mediaDevices .getUserMedia({ video: videoConstraints, audio: audioConstraints, }) .then((stream) => { const audioTracks = stream.getAudioTracks(); const videoTracks = stream.getVideoTracks(); videoElement.srcObject = stream; if (audioTracks.length > 0) { audioTrack = audioTracks[0]; } if (videoTracks.length > 0) { videoTrack = videoTracks[0]; } }) .then(() => { return new Promise((resolve) => { videoElement.onloadedmetadata = resolve; }); }) .then(() => { getCurrentSettings(); }) .catch(handleError); } </code></pre></div> <p>There are several steps here:</p> <ol> <li>It calls <code>buildConstraints()</code> to create the <a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a> objects for the two tracks from the code in the edit boxes.</li> <li>It calls <a href="/en-US/docs/Web/API/MediaDevices/getUserMedia" title="navigator.mediaDevices.getUserMedia()"><code>navigator.mediaDevices.getUserMedia()</code></a>, passing in the constraints objects for the video and audio tracks. This returns a <a href="/en-US/docs/Web/API/MediaStream"><code>MediaStream</code></a> with the audio and video from a source matching the inputs (typically a webcam, although if you provide the right constraints you can get media from other sources).</li> <li>When the stream is obtained, it's attached to the <a href="/en-US/docs/Web/HTML/Element/video"><code><video></code></a> element so that it's visible on screen, and we grab the audio track and video track into the variables <code>audioTrack</code> and <code>videoTrack</code>.</li> <li>Then we set up a promise which resolves when the <a href="/en-US/docs/Web/API/HTMLMediaElement/loadedmetadata_event" title="loadedmetadata"><code>loadedmetadata</code></a> event occurs on the video element.</li> <li>When that happens, we know the video has started playing, so we call our <code>getCurrentSettings()</code> function (described above) to display the actual settings that the browser decided upon after considering our constraints and the capabilities of the hardware.</li> <li>If an error occurs, we log it using the <code>handleError()</code> method that we'll look at farther down in this article.</li> </ol> <p>We also need to set up an event listener to watch for the "Start Video" button to be clicked:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>document.getElementById("startButton").addEventListener( "click", () => { startVideo(); }, false, ); </code></pre></div></div></section><section aria-labelledby="applying_constraint_set_updates"><h3 id="applying_constraint_set_updates"><a href="#applying_constraint_set_updates">Applying constraint set updates</a></h3><div class="section-content"><p>Next, we set up an event listener for the "Apply Constraints" button. If it's clicked and there's not already media in use, we call <code>startVideo()</code>, and let that function handle starting the stream with the specified settings in place. Otherwise, we follow these steps to apply the updated constraints to the already-active stream:</p> <ol> <li><code>buildConstraints()</code> is called to construct updated <a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a> objects for the audio track (<code>audioConstraints</code>) and the video track (<code>videoConstraints</code>).</li> <li><a href="/en-US/docs/Web/API/MediaStreamTrack/applyConstraints"><code>MediaStreamTrack.applyConstraints()</code></a> is called on the video track (if there is one) to apply the new <code>videoConstraints</code>. If this succeeds, the contents of the video track's current settings box are updated based on the result of calling its <a href="/en-US/docs/Web/API/MediaStreamTrack/getSettings" title="getSettings()"><code>getSettings()</code></a> method.</li> <li>Once that's done, <code>applyConstraints()</code> is called on the audio track (if there is one) to apply the new audio constraints. If this succeeds, the contents of the audio track's current settings box are updated based on the result of calling its <a href="/en-US/docs/Web/API/MediaStreamTrack/getSettings" title="getSettings()"><code>getSettings()</code></a> method.</li> <li>If an error occurs applying either set of constraints, <code>handleError()</code> is used to output a message into the log.</li> </ol> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>document.getElementById("applyButton").addEventListener( "click", () => { if (!videoTrack && !audioTrack) { startVideo(); } else { buildConstraints(); const prettyJson = (obj) => JSON.stringify(obj, null, 2); if (videoTrack) { videoTrack .applyConstraints(videoConstraints) .then(() => { videoSettingsText.value = prettyJson(videoTrack.getSettings()); }) .catch(handleError); } if (audioTrack) { audioTrack .applyConstraints(audioConstraints) .then(() => { audioSettingsText.value = prettyJson(audioTrack.getSettings()); }) .catch(handleError); } } }, false, ); </code></pre></div></div></section><section aria-labelledby="handling_the_stop_button"><h3 id="handling_the_stop_button"><a href="#handling_the_stop_button">Handling the stop button</a></h3><div class="section-content"><p>Then we set up the handler for the stop button.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>document.getElementById("stopButton").addEventListener("click", () => { if (videoTrack) { videoTrack.stop(); } if (audioTrack) { audioTrack.stop(); } videoTrack = audioTrack = null; videoElement.srcObject = null; }); </code></pre></div> <p>This stops the active tracks, sets the <code>videoTrack</code> and <code>audioTrack</code> variables to <code>null</code> so we know they're gone, and removes the stream from the <a href="/en-US/docs/Web/HTML/Element/video"><code><video></code></a> element by setting <a href="/en-US/docs/Web/API/HTMLMediaElement/srcObject"><code>HTMLMediaElement.srcObject</code></a> to <code>null</code>.</p></div></section><section aria-labelledby="simple_tab_support_in_the_editor"><h3 id="simple_tab_support_in_the_editor"><a href="#simple_tab_support_in_the_editor">Simple tab support in the editor</a></h3><div class="section-content"><p>This code adds simple support for tabs to the <a href="/en-US/docs/Web/HTML/Element/textarea"><code><textarea></code></a> elements by making the tab key insert two space characters when either constraint edit box is focused.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function keyDownHandler(event) { if (event.key === "Tab") { const elem = event.target; const str = elem.value; const position = elem.selectionStart; const beforeTab = str.substring(0, position); const afterTab = str.substring(position, str.length); const newStr = `${beforeTab} ${afterTab}`; elem.value = newStr; elem.selectionStart = elem.selectionEnd = position + 2; event.preventDefault(); } } videoConstraintEditor.addEventListener("keydown", keyDownHandler, false); audioConstraintEditor.addEventListener("keydown", keyDownHandler, false); </code></pre></div></div></section><section aria-labelledby="show_constrainable_properties_the_browser_supports"><h3 id="show_constrainable_properties_the_browser_supports"><a href="#show_constrainable_properties_the_browser_supports">Show constrainable properties the browser supports</a></h3><div class="section-content"><p>The last significant piece of the puzzle: code that displays, for the user's reference, a list of the constrainable properties which their browser supports. Each property is a link to its documentation on MDN for the user's convenience. See the <a href="/en-US/docs/Web/API/MediaDevices/getSupportedConstraints#examples"><code>MediaDevices.getSupportedConstraints()</code> examples</a> for details on how this code works.</p> <div class="notecard note"> <p><strong>Note:</strong> Of course, there may be non-standard properties in this list, in which case you probably will find that the documentation link doesn't help much.</p> </div> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const supportedConstraints = navigator.mediaDevices.getSupportedConstraints(); for (const constraint in supportedConstraints) { if (Object.hasOwn(supportedConstraints, constraint)) { const elem = document.createElement("li"); elem.innerHTML = `<code><a href='https://developer.mozilla.org/docs/Web/API/MediaTrackSupportedConstraints/${constraint}' target='_blank'>${constraint}</a></code>`; supportedConstraintList.appendChild(elem); } } </code></pre></div></div></section><section aria-labelledby="error_handling"><h3 id="error_handling"><a href="#error_handling">Error handling</a></h3><div class="section-content"><p>We also have some simple error handling code; <code>handleError()</code> is called to handle promises which fail, and the <code>log()</code> function appends the error message to a special logging <a href="/en-US/docs/Web/HTML/Element/div"><code><div></code></a> box under the video.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function log(msg) { logElement.innerHTML += `${msg}<br>`; } function handleError(reason) { log( `Error <code>${reason.name}</code> in constraint <code>${reason.constraint}</code>: ${reason.message}`, ); } </code></pre></div></div></section><section aria-labelledby="result"><h3 id="result"><a href="#result">Result</a></h3><div class="section-content"><p>Here you can see the complete example in action.</p><div class="code-example"><div class="example-header"></div><iframe class="sample-code-frame" title="Example Constraint exerciser sample" id="frame_example_constraint_exerciser" width="650" height="800" src="about:blank" data-live-path="/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints" data-live-id="example_constraint_exerciser" sandbox="allow-same-origin allow-scripts" loading="lazy"></iframe></div></div></section><h2 id="specifications"><a href="#specifications">Specifications</a></h2><table class="standard-table"><thead><tr><th scope="col">Specification</th></tr></thead><tbody><tr><td><a href="https://w3c.github.io/mediacapture-main/#dom-mediadevices-getsupportedconstraints">Media Capture and Streams <br/><small># dom-mediadevices-getsupportedconstraints</small></a></td></tr></tbody></table><h2 id="browser_compatibility"><a href="#browser_compatibility">Browser compatibility</a></h2><p>BCD tables only load in the browser<noscript> with JavaScript enabled. Enable JavaScript to view data.</noscript></p><section aria-labelledby="see_also"><h2 id="see_also"><a href="#see_also">See also</a></h2><div class="section-content"><ul> <li><a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API">Media Capture and Streams API</a></li> <li><a href="/en-US/docs/Web/API/MediaTrackConstraints"><code>MediaTrackConstraints</code></a></li> <li><a href="/en-US/docs/Web/API/MediaTrackSettings"><code>MediaTrackSettings</code></a></li> <li><a href="/en-US/docs/Web/API/MediaDevices/getSupportedConstraints"><code>MediaDevices.getSupportedConstraints()</code></a></li> <li><a href="/en-US/docs/Web/API/MediaStreamTrack/applyConstraints"><code>MediaStreamTrack.applyConstraints()</code></a></li> <li><a href="/en-US/docs/Web/API/MediaStreamTrack/getSettings"><code>MediaStreamTrack.getSettings()</code></a></li> </ul></div></section></article><aside class="article-footer"><div class="article-footer-inner"><div class="svg-container"><svg xmlns="http://www.w3.org/2000/svg" width="162" height="162" viewBox="0 0 162 162" fill="none" role="none"><mask id="b" fill="#fff"><path d="M97.203 47.04c8.113-7.886 18.004-13.871 28.906-17.492a78 78 0 0 1 33.969-3.39c11.443 1.39 22.401 5.295 32.024 11.411s17.656 14.28 23.476 23.86c5.819 9.579 9.269 20.318 10.083 31.385a69.85 69.85 0 0 1-5.387 32.44c-4.358 10.272-11.115 19.443-19.747 26.801-8.632 7.359-18.908 12.709-30.034 15.637l-6.17-21.698c7.666-2.017 14.746-5.703 20.694-10.773 5.948-5.071 10.603-11.389 13.606-18.467a48.14 48.14 0 0 0 3.712-22.352c-.561-7.625-2.938-15.025-6.948-21.625s-9.544-12.226-16.175-16.44-14.181-6.904-22.065-7.863a53.75 53.75 0 0 0-23.405 2.336c-7.513 2.495-14.327 6.62-19.918 12.053z"></path></mask><path stroke="url(#a)" stroke-dasharray="6, 6" stroke-width="2" d="M97.203 47.04c8.113-7.886 18.004-13.871 28.906-17.492a78 78 0 0 1 33.969-3.39c11.443 1.39 22.401 5.295 32.024 11.411s17.656 14.28 23.476 23.86c5.819 9.579 9.269 20.318 10.083 31.385a69.85 69.85 0 0 1-5.387 32.44c-4.358 10.272-11.115 19.443-19.747 26.801-8.632 7.359-18.908 12.709-30.034 15.637l-6.17-21.698c7.666-2.017 14.746-5.703 20.694-10.773 5.948-5.071 10.603-11.389 13.606-18.467a48.14 48.14 0 0 0 3.712-22.352c-.561-7.625-2.938-15.025-6.948-21.625s-9.544-12.226-16.175-16.44-14.181-6.904-22.065-7.863a53.75 53.75 0 0 0-23.405 2.336c-7.513 2.495-14.327 6.62-19.918 12.053z" mask="url(#b)" style="stroke:url(#a)" transform="translate(-63.992 -25.587)"></path><ellipse cx="8.066" cy="111.597" fill="var(--background-tertiary)" rx="53.677" ry="53.699" transform="matrix(.71707 -.697 .7243 .6895 0 0)"></ellipse><g clip-path="url(#c)" transform="translate(-63.992 -25.587)"><path fill="#9abff5" d="m144.256 137.379 32.906 12.434a4.41 4.41 0 0 1 2.559 5.667l-9.326 24.679a4.41 4.41 0 0 1-5.667 2.559l-8.226-3.108-2.332 6.17c-.466 1.233-.375 1.883-1.609 1.417l-2.253-.527c-.411-.155-.95-.594-1.206-1.161l-4.734-10.484-12.545-4.741a4.41 4.41 0 0 1-2.559-5.667l9.325-24.679a4.41 4.41 0 0 1 5.667-2.559m9.961 29.617 8.227 3.108 3.264-8.638-.498-6.768-4.113-1.555.548 7.258-4.319-1.632zm-12.339-4.663 8.226 3.108 3.264-8.637-.498-6.769-4.113-1.554.548 7.257-4.319-1.632z"></path></g><g clip-path="url(#d)" transform="translate(-63.992 -25.587)"><path fill="#81b0f3" d="M135.35 60.136 86.67 41.654c-3.346-1.27-7.124.428-8.394 3.775L64.414 81.938c-1.27 3.347.428 7.125 3.774 8.395l12.17 4.62-3.465 9.128c-.693 1.826-1.432 2.457.394 3.15l3.014 1.625c.609.231 1.637.274 2.477-.104l15.53-6.983 18.56 7.047c3.346 1.27 7.124-.428 8.395-3.775l13.862-36.51c1.27-3.346-.428-7.124-3.775-8.395M95.261 83.207l-12.17-4.62 4.852-12.779 7.19-7.017 6.085 2.31-7.725 7.51 6.389 2.426zm18.255 6.93-12.17-4.62 4.852-12.778 7.189-7.017 6.085 2.31-7.725 7.51 6.39 2.426z"></path></g><defs><clipPath id="c"><path fill="#fff" d="m198.638 146.586-65.056-24.583-24.583 65.057 65.056 24.582z"></path></clipPath><clipPath id="d"><path fill="#fff" d="m66.438 14.055 96.242 36.54-36.54 96.243-96.243-36.54z"></path></clipPath><linearGradient id="a" x1="97.203" x2="199.995" y1="47.04" y2="152.793" gradientUnits="userSpaceOnUse"><stop stop-color="#086DFC"></stop><stop offset="0.246" stop-color="#2C81FA"></stop><stop offset="0.516" stop-color="#5497F8"></stop><stop offset="0.821" stop-color="#80B0F6"></stop><stop offset="1" stop-color="#9ABFF5"></stop></linearGradient></defs></svg></div><h2>Help improve MDN</h2><fieldset class="feedback"><label>Was this page helpful to you?</label><div class="button-container"><button type="button" class="button primary has-icon yes"><span class="button-wrap"><span class="icon icon-thumbs-up "></span>Yes</span></button><button type="button" class="button primary has-icon no"><span class="button-wrap"><span class="icon icon-thumbs-down "></span>No</span></button></div></fieldset><a class="contribute" href="https://github.com/mdn/content/blob/main/CONTRIBUTING.md" title="This will take you to our contribution guidelines on GitHub." target="_blank" rel="noopener noreferrer">Learn how to contribute</a>.<p class="last-modified-date">This page was last modified on <time dateTime="2024-10-27T23:53:01.000Z">Oct 27, 2024</time> by <a href="/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints/contributors.txt" rel="nofollow">MDN contributors</a>.</p><div id="on-github" class="on-github"><a href="https://github.com/mdn/content/blob/main/files/en-us/web/api/media_capture_and_streams_api/constraints/index.md?plain=1" title="Folder: en-us/web/api/media_capture_and_streams_api/constraints (Opens in a new tab)" target="_blank" rel="noopener noreferrer">View this page on GitHub</a> • <a href="https://github.com/mdn/content/issues/new?template=page-report.yml&mdn-url=https%3A%2F%2Fdeveloper.mozilla.org%2Fen-US%2Fdocs%2FWeb%2FAPI%2FMedia_Capture_and_Streams_API%2FConstraints&metadata=%3C%21--+Do+not+make+changes+below+this+line+--%3E%0A%3Cdetails%3E%0A%3Csummary%3EPage+report+details%3C%2Fsummary%3E%0A%0A*+Folder%3A+%60en-us%2Fweb%2Fapi%2Fmedia_capture_and_streams_api%2Fconstraints%60%0A*+MDN+URL%3A+https%3A%2F%2Fdeveloper.mozilla.org%2Fen-US%2Fdocs%2FWeb%2FAPI%2FMedia_Capture_and_Streams_API%2FConstraints%0A*+GitHub+URL%3A+https%3A%2F%2Fgithub.com%2Fmdn%2Fcontent%2Fblob%2Fmain%2Ffiles%2Fen-us%2Fweb%2Fapi%2Fmedia_capture_and_streams_api%2Fconstraints%2Findex.md%0A*+Last+commit%3A+https%3A%2F%2Fgithub.com%2Fmdn%2Fcontent%2Fcommit%2Fbff3a6a2e6b3c13dd8bb0c80a1eb9da08cce5dc6%0A*+Document+last+modified%3A+2024-10-27T23%3A53%3A01.000Z%0A%0A%3C%2Fdetails%3E" title="This will take you to GitHub to file a new issue." target="_blank" rel="noopener noreferrer">Report a problem with this content</a></div></div></aside></main></div></div><footer id="nav-footer" class="page-footer"><div class="page-footer-grid"><div class="page-footer-logo-col"><a href="/" class="mdn-footer-logo" aria-label="MDN homepage"><svg width="48" height="17" viewBox="0 0 48 17" fill="none" xmlns="http://www.w3.org/2000/svg"><title id="mdn-footer-logo-svg">MDN logo</title><path d="M20.04 16.512H15.504V10.416C15.504 9.488 15.344 8.824 15.024 8.424C14.72 8.024 14.264 7.824 13.656 7.824C12.92 7.824 12.384 8.064 12.048 8.544C11.728 9.024 11.568 9.64 11.568 10.392V14.184H13.008V16.512H8.472V10.416C8.472 9.488 8.312 8.824 7.992 8.424C7.688 8.024 7.232 7.824 6.624 7.824C5.872 7.824 5.336 8.064 5.016 8.544C4.696 9.024 4.536 9.64 4.536 10.392V14.184H6.6V16.512H0V14.184H1.44V8.04H0.024V5.688H4.536V7.32C5.224 6.088 6.32 5.472 7.824 5.472C8.608 5.472 9.328 5.664 9.984 6.048C10.64 6.432 11.096 7.016 11.352 7.8C11.992 6.248 13.168 5.472 14.88 5.472C15.856 5.472 16.72 5.776 17.472 6.384C18.224 6.992 18.6 7.936 18.6 9.216V14.184H20.04V16.512Z" fill="currentColor"></path><path d="M33.6714 16.512H29.1354V14.496C28.8314 15.12 28.3834 15.656 27.7914 16.104C27.1994 16.536 26.4154 16.752 25.4394 16.752C24.0154 16.752 22.8954 16.264 22.0794 15.288C21.2634 14.312 20.8554 12.984 20.8554 11.304C20.8554 9.688 21.2554 8.312 22.0554 7.176C22.8554 6.04 24.0634 5.472 25.6794 5.472C26.5594 5.472 27.2794 5.648 27.8394 6C28.3994 6.352 28.8314 6.8 29.1354 7.344V2.352H26.9754V0H32.2314V14.184H33.6714V16.512ZM29.1354 11.04V10.776C29.1354 9.88 28.8954 9.184 28.4154 8.688C27.9514 8.176 27.3674 7.92 26.6634 7.92C25.9754 7.92 25.3674 8.176 24.8394 8.688C24.3274 9.2 24.0714 10.008 24.0714 11.112C24.0714 12.152 24.3114 12.944 24.7914 13.488C25.2714 14.032 25.8394 14.304 26.4954 14.304C27.3114 14.304 27.9514 13.96 28.4154 13.272C28.8954 12.584 29.1354 11.84 29.1354 11.04Z" fill="currentColor"></path><path d="M47.9589 16.512H41.9829V14.184H43.4229V10.416C43.4229 9.488 43.2629 8.824 42.9429 8.424C42.6389 8.024 42.1829 7.824 41.5749 7.824C40.8389 7.824 40.2709 8.056 39.8709 8.52C39.4709 8.968 39.2629 9.56 39.2469 10.296V14.184H40.6869V16.512H34.7109V14.184H36.1509V8.04H34.5909V5.688H39.2469V7.344C39.9669 6.096 41.1269 5.472 42.7269 5.472C43.7509 5.472 44.6389 5.776 45.3909 6.384C46.1429 6.992 46.5189 7.936 46.5189 9.216V14.184H47.9589V16.512Z" fill="currentColor"></path></svg></a><p>Your blueprint for a better internet.</p><ul class="social-icons"><li><a href="https://mozilla.social/@mdn" target="_blank" rel="me noopener noreferrer"><span class="icon icon-mastodon"></span><span class="visually-hidden">MDN on Mastodon</span></a></li><li><a href="https://twitter.com/mozdevnet" target="_blank" rel="noopener noreferrer"><span class="icon icon-twitter-x"></span><span class="visually-hidden">MDN on X (formerly Twitter)</span></a></li><li><a href="https://github.com/mdn/" target="_blank" rel="noopener noreferrer"><span class="icon icon-github-mark-small"></span><span class="visually-hidden">MDN on GitHub</span></a></li><li><a href="/en-US/blog/rss.xml" target="_blank"><span class="icon icon-feed"></span><span class="visually-hidden">MDN Blog RSS Feed</span></a></li></ul></div><div class="page-footer-nav-col-1"><h2 class="footer-nav-heading">MDN</h2><ul class="footer-nav-list"><li class="footer-nav-item"><a href="/en-US/about">About</a></li><li class="footer-nav-item"><a href="/en-US/blog/">Blog</a></li><li class="footer-nav-item"><a href="https://www.mozilla.org/en-US/careers/listings/?team=ProdOps" target="_blank" rel="noopener noreferrer">Careers</a></li><li class="footer-nav-item"><a href="/en-US/advertising">Advertise with us</a></li></ul></div><div class="page-footer-nav-col-2"><h2 class="footer-nav-heading">Support</h2><ul class="footer-nav-list"><li class="footer-nav-item"><a class="footer-nav-link" href="https://support.mozilla.org/products/mdn-plus">Product help</a></li><li class="footer-nav-item"><a class="footer-nav-link" href="/en-US/docs/MDN/Community/Issues">Report an issue</a></li></ul></div><div class="page-footer-nav-col-3"><h2 class="footer-nav-heading">Our communities</h2><ul class="footer-nav-list"><li class="footer-nav-item"><a class="footer-nav-link" href="/en-US/community">MDN Community</a></li><li class="footer-nav-item"><a class="footer-nav-link" href="https://discourse.mozilla.org/c/mdn/236" target="_blank" rel="noopener noreferrer">MDN Forum</a></li><li class="footer-nav-item"><a class="footer-nav-link" href="/discord" target="_blank" rel="noopener noreferrer">MDN Chat</a></li></ul></div><div class="page-footer-nav-col-4"><h2 class="footer-nav-heading">Developers</h2><ul class="footer-nav-list"><li class="footer-nav-item"><a class="footer-nav-link" href="/en-US/docs/Web">Web Technologies</a></li><li class="footer-nav-item"><a class="footer-nav-link" href="/en-US/docs/Learn">Learn Web Development</a></li><li class="footer-nav-item"><a class="footer-nav-link" href="/en-US/plus">MDN Plus</a></li><li class="footer-nav-item"><a href="https://hacks.mozilla.org/" target="_blank" rel="noopener noreferrer">Hacks Blog</a></li></ul></div><div class="page-footer-moz"><a href="https://www.mozilla.org/" class="footer-moz-logo-link" target="_blank" rel="noopener noreferrer"><svg width="112" height="32" fill="none" xmlns="http://www.w3.org/2000/svg"><title id="mozilla-footer-logo-svg">Mozilla logo</title><path d="M41.753 14.218c-2.048 0-3.324 1.522-3.324 4.157 0 2.423 1.119 4.286 3.29 4.286 2.082 0 3.447-1.678 3.447-4.347 0-2.826-1.522-4.096-3.413-4.096Zm54.89 7.044c0 .901.437 1.618 1.645 1.618 1.427 0 2.949-1.024 3.044-3.352-.649-.095-1.365-.185-2.02-.185-1.426-.005-2.668.397-2.668 1.92Z" fill="currentColor"></path><path d="M0 0v32h111.908V0H0Zm32.56 25.426h-5.87v-7.884c0-2.423-.806-3.352-2.39-3.352-1.924 0-2.702 1.365-2.702 3.324v4.868h1.864v3.044h-5.864v-7.884c0-2.423-.806-3.352-2.39-3.352-1.924 0-2.702 1.365-2.702 3.324v4.868h2.669v3.044H6.642v-3.044h1.863v-7.918H6.642V11.42h5.864v2.11c.839-1.489 2.3-2.39 4.252-2.39 2.02 0 3.878.963 4.566 3.01.778-1.862 2.361-3.01 4.566-3.01 2.512 0 4.812 1.522 4.812 4.84v6.402h1.863v3.044h-.005Zm9.036.307c-4.314 0-7.296-2.635-7.296-7.106 0-4.096 2.484-7.481 7.514-7.481s7.481 3.38 7.481 7.29c0 4.472-3.228 7.297-7.699 7.297Zm22.578-.307H51.942l-.403-2.11 7.7-8.846h-4.376l-.621 2.17-2.888-.313.498-4.907h12.294l.313 2.11-7.767 8.852h4.533l.654-2.172 3.167.308-.872 4.908Zm7.99 0h-4.191v-5.03h4.19v5.03Zm0-8.976h-4.191v-5.03h4.19v5.03Zm2.618 8.976 6.054-21.358h3.945l-6.054 21.358h-3.945Zm8.136 0 6.048-21.358h3.945l-6.054 21.358h-3.939Zm21.486.307c-1.863 0-2.887-1.085-3.072-2.792-.805 1.427-2.232 2.792-4.498 2.792-2.02 0-4.314-1.085-4.314-4.006 0-3.447 3.323-4.253 6.518-4.253.778 0 1.584.034 2.3.124v-.465c0-1.427-.034-3.133-2.3-3.133-.84 0-1.488.061-2.143.402l-.453 1.578-3.195-.34.549-3.224c2.45-.996 3.692-1.27 5.992-1.27 3.01 0 5.556 1.55 5.556 4.75v6.083c0 .805.314 1.085.963 1.085.184 0 .375-.034.587-.095l.034 2.11a5.432 5.432 0 0 1-2.524.654Z" fill="currentColor"></path></svg></a><ul class="footer-moz-list"><li class="footer-moz-item"><a href="https://www.mozilla.org/privacy/websites/" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Website Privacy Notice</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/privacy/websites/#cookies" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Cookies</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/legal/terms/mozilla" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Legal</a></li><li class="footer-moz-item"><a href="https://www.mozilla.org/about/governance/policies/participation/" class="footer-moz-link" target="_blank" rel="noopener noreferrer">Community Participation Guidelines</a></li></ul></div><div class="page-footer-legal"><p id="license" class="page-footer-legal-text">Visit <a href="https://www.mozilla.org" target="_blank" rel="noopener noreferrer">Mozilla Corporation’s</a> not-for-profit parent, the <a target="_blank" rel="noopener noreferrer" href="https://foundation.mozilla.org/">Mozilla Foundation</a>.<br/>Portions of this content are ©1998–2024 by individual mozilla.org contributors. Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"Capabilities, constraints, and settings","mdn_url":"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints","locale":"en-US","native":"English (US)","browserCompat":["api.MediaDevices.getSupportedConstraints"],"sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Web/API/Media_Capture_and_Streams_API\">Media Capture and Streams API</a></li><li class=\"toggle\"><details open=\"\"><summary>Guides</summary><ol><li><em><a href=\"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints\" aria-current=\"page\">Capabilities, constraints, and settings</a></em></li><li><a href=\"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Taking_still_photos\">Taking still photos with getUserMedia()</a></li></ol></details></li><li class=\"toggle\"><details open=\"\"><summary>Interfaces</summary><ol><li><a href=\"/en-US/docs/Web/API/CanvasCaptureMediaStreamTrack\"><code>CanvasCaptureMediaStreamTrack</code></a></li><li><a href=\"/en-US/docs/Web/API/InputDeviceInfo\"><code>InputDeviceInfo</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaDeviceInfo\"><code>MediaDeviceInfo</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaDevices\"><code>MediaDevices</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaStream\"><code>MediaStream</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaStreamTrackEvent\"><code>MediaStreamTrackEvent</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaTrackSettings\"><code>MediaTrackSettings</code></a></li><li><a href=\"/en-US/docs/Web/API/MediaTrackSupportedConstraints\"><code>MediaTrackSupportedConstraints</code></a></li><li><a href=\"/en-US/docs/Web/API/OverconstrainedError\"><code>OverconstrainedError</code></a></li></ol></details></li><li class=\"toggle\"><details open=\"\"><summary>Properties</summary><ol><li><a href=\"/en-US/docs/Web/API/Navigator/mediaDevices\"><code>Navigator.mediaDevices</code></a></li></ol></details></li><li class=\"toggle\"><details open=\"\"><summary>Methods</summary><ol><li><a href=\"/en-US/docs/Web/API/HTMLCanvasElement/captureStream\"><code>HTMLCanvasElement.captureStream()</code></a></li><li><a href=\"/en-US/docs/Web/API/HTMLMediaElement/captureStream\"><code>HTMLMediaElement.captureStream()</code></a></li></ol></details></li></ol>","sidebarMacro":"DefaultAPISidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<p>This article discusses the twin concepts of <strong>constraints</strong> and <strong>capabilities</strong>, as well as media settings, and includes an example we call the <a href=\"#example_constraint_exerciser\">Constraint Exerciser</a>. The Constraint Exerciser lets you experiment with the results of different constraint sets being applied to the audio and video tracks coming from the computer's A/V input devices (such as its webcam and microphone).</p>\n<p>Historically, writing scripts for the Web that work intimately with Web APIs has had a well-known challenge: often, your code needs to know whether or not an API exists and if so, what its limitations are on the <a href=\"/en-US/docs/Glossary/User_agent\">user agent</a> it's running on. Figuring this out has often been difficult, and has usually involved looking at some combination of which <a href=\"/en-US/docs/Glossary/User_agent\">user agent</a> (or browser) you're running on, which version it is, looking to see if certain objects exist, trying to see whether various things work or not and determining what errors occur, and so forth. The result has been a lot of very fragile code, or a reliance on libraries which figure this stuff out for you, then implement <a href=\"/en-US/docs/Glossary/Polyfill\">polyfills</a> to patch the holes in the implementation on your behalf.</p>\n<p>Capabilities and constraints let the browser and website or app exchange information about what <strong>constrainable properties</strong> the browser's implementation supports and what values it supports for each.</p>"}},{"type":"prose","value":{"id":"overview","title":"Overview","isH3":false,"content":"<p>The process works like this (using <a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a> as an example):</p>\n<ol>\n <li>If needed, call <a href=\"/en-US/docs/Web/API/MediaDevices/getSupportedConstraints\"><code>MediaDevices.getSupportedConstraints()</code></a> to get the list of <strong>supported constraints</strong>, which tells you what constrainable properties the browser knows about. This isn't always necessary, since any that aren't known will be ignored when you specify them—but if you have any that you can't get by without, you can start by checking to be sure they're on the list.</li>\n <li>Once the script knows whether the property or properties it wishes to use are supported, it can then check the <strong>capabilities</strong> of the API and its implementation by examining the object returned by the track's <code>getCapabilities()</code> method; this object lists each supported constraint and the values or range of values which are supported.</li>\n <li>Finally, the track's <code>applyConstraints()</code> method is called to configure the API as desired by specifying the values or ranges of values it wishes to use for any of the constrainable properties about which it has a preference.</li>\n <li>The track's <code>getConstraints()</code> method returns the set of constraints passed into the most recent call to <code>applyConstraints()</code>. This may not represent the actual current state of the track, due to properties whose requested values had to be adjusted and because platform default values aren't represented. For a complete representation of the track's current configuration, use <code>getSettings()</code>.</li>\n</ol>\n<p>In the Media Capture and Streams API, both <a href=\"/en-US/docs/Web/API/MediaStream\"><code>MediaStream</code></a> and <a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a> have constrainable properties.</p>"}},{"type":"prose","value":{"id":"determining_if_a_constraint_is_supported","title":"Determining if a constraint is supported","isH3":false,"content":"<p>If you need to know whether or not a given constraint is supported by the user agent, you can find out by calling <a href=\"/en-US/docs/Web/API/MediaDevices/getSupportedConstraints\" title=\"navigator.mediaDevices.getSupportedConstraints()\"><code>navigator.mediaDevices.getSupportedConstraints()</code></a> to get a list of the constrainable properties which the browser knows, like this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const supported = navigator.mediaDevices.getSupportedConstraints();\n\ndocument.getElementById(\"frameRateSlider\").disabled = !supported[\"frameRate\"];\n</code></pre></div>\n<p>In this example, the supported constraints are fetched, and a control that lets the user configure the frame rate is disabled if the <code>frameRate</code> constraint isn't supported.</p>"}},{"type":"prose","value":{"id":"how_constraints_are_defined","title":"How constraints are defined","isH3":false,"content":"<p>A single constraint is an object whose name matches the constrainable property whose desired value or range of values is being specified. This object contains zero or more individual constraints, as well as an optional sub-object named <code>advanced</code>, which contains another set of zero or more constraints which the user agent must satisfy if at all possible. The user agent attempts to satisfy constraints in the order specified in the constraint set.</p>\n<p>The most important thing to understand is that most constraints aren't requirements; instead, they're requests. There are exceptions, and we'll get to those shortly.</p>"}},{"type":"prose","value":{"id":"requesting_a_specific_value_for_a_setting","title":"Requesting a specific value for a setting","isH3":true,"content":"<p>Most, each constraint may be a specific value indicating a desired value for the setting. For example:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const constraints = {\n width: 1920,\n height: 1080,\n aspectRatio: 1.777777778,\n};\n\nmyTrack.applyConstraints(constraints);\n</code></pre></div>\n<p>In this case, the constraints indicate that any values are fine for nearly all properties, but that a standard high definition (HD) video size is desired, with the standard 16:9 <a href=\"/en-US/docs/Glossary/Aspect_ratio\">aspect ratio</a>. There's no guarantee that the resulting track will match any of these, but the user agent should do its best to match as many as possible.</p>\n<p>The prioritization of the properties is simple: if two properties' requested values are mutually exclusive, then the one listed first in the constraint set will be used. As an example, if the browser running the code above couldn't provide a 1920x1080 track but could do 1920x900, then that's what would be provided.</p>\n<p>Simple constraints like these, specifying a single value, are always treated as non-required. The user agent will try to provide what you request but will not guarantee that what you get will match. However, if you use simple values for properties when calling <a href=\"/en-US/docs/Web/API/MediaStreamTrack/applyConstraints\"><code>MediaStreamTrack.applyConstraints()</code></a>, the request will always succeed, because these values will be considered a request, not a requirement.</p>"}},{"type":"prose","value":{"id":"specifying_a_range_of_values","title":"Specifying a range of values","isH3":true,"content":"<p>Sometimes, any value within a range is acceptable for a property's value. You can specify ranges with either or both minimum and maximum values, and you can even specify an ideal value within the range, if you choose. If you provide an ideal value, the browser will try to get as close as possible to matching that value, given the other constraints specified.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const supports = navigator.mediaDevices.getSupportedConstraints();\n\nif (\n !supports[\"width\"] ||\n !supports[\"height\"] ||\n !supports[\"frameRate\"] ||\n !supports[\"facingMode\"]\n) {\n // We're missing needed properties, so handle that error.\n} else {\n const constraints = {\n width: { min: 640, ideal: 1920, max: 1920 },\n height: { min: 400, ideal: 1080 },\n aspectRatio: 1.777777778,\n frameRate: { max: 30 },\n facingMode: { exact: \"user\" },\n };\n\n myTrack\n .applyConstraints(constraints)\n .then(() => {\n /* do stuff if constraints applied successfully */\n })\n .catch((reason) => {\n /* failed to apply constraints; reason is why */\n });\n}\n</code></pre></div>\n<p>Here, after ensuring that the constrainable properties for which matches must be found are supported (<code>width</code>, <code>height</code>, <code>frameRate</code>, and <code>facingMode</code>), we set up constraints which request a width no smaller than 640 and no larger than 1920 (but preferably 1920), a height no smaller than 400 (but ideally 1080), an aspect ratio of 16:9 (1.777777778), and a frame rate no greater than 30 frames per second. In addition, the only acceptable input device is a camera facing the user (a \"selfie cam\"). If the <code>width</code>, <code>height</code>, <code>frameRate</code>, or <code>facingMode</code> constraints can't be met, the promise returned by <code>applyConstraints()</code> will be rejected.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> Constraints which are specified using any or all of <code>max</code>, <code>min</code>, or <code>exact</code> are always treated as mandatory. If any constraint which uses one or more of those can't be met when calling <code>applyConstraints()</code>, the promise will be rejected.</p>\n</div>"}},{"type":"prose","value":{"id":"advanced_constraints","title":"Advanced constraints","isH3":true,"content":"<p>So-called advanced constraints are created by adding an <code>advanced</code> property to the constraint set; this property's value is an array of additional constraint sets which are considered optional. There are few if any use cases for this feature, and there is some interest in removing it from the specification, so it will not be discussed here. If you wish to learn more, see <a href=\"https://www.w3.org/TR/mediacapture-streams/#idl-def-Constraints\" class=\"external\" target=\"_blank\">section 11 of the Media Capture and Streams specification</a>, past example 2.</p>"}},{"type":"prose","value":{"id":"checking_capabilities","title":"Checking capabilities","isH3":false,"content":"<p>You can call <a href=\"/en-US/docs/Web/API/MediaStreamTrack/getCapabilities\"><code>MediaStreamTrack.getCapabilities()</code></a> to get a list of all of the supported capabilities and the values or ranges of values which each one accepts on the current platform and user agent. This function returns an object which lists each constrainable property supported by the browser and a value or range of values which are supported for each one of those properties.</p>\n<p>For example, the following snippet will result in the user being asked for permission to access their local camera and microphone. Once permission is granted, <code>MediaTrackCapabilities</code> objects will be logged to the console that detail the capabilities of each <a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>navigator.mediaDevices\n .getUserMedia({ video: true, audio: true })\n .then((stream) => {\n const tracks = stream.getTracks();\n tracks.map((t) => console.log(t.getCapabilities()));\n });\n</code></pre></div>\n<p>An example capabilities object looks like this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>{\n \"autoGainControl\": [\n true,\n false\n ],\n \"channelCount\": {\n \"max\": 1,\n \"min\": 1\n },\n \"deviceId\": \"jjxEMqxIhGdryqbTjDrXPWrkjy55Vte70kWpMe3Lge8=\",\n \"echoCancellation\": [\n true,\n false\n ],\n \"groupId\": \"o2tZiEj4MwOdG/LW3HwkjpLm1D8URat4C5kt742xrVQ=\",\n \"noiseSuppression\": [\n true,\n false\n ]\n}\n</code></pre></div>\n<p>The exact contents of the object will depend on the browser and media hardware.</p>"}},{"type":"prose","value":{"id":"applying_constraints","title":"Applying constraints","isH3":false,"content":"<p>The first and most common way to use constraints is to specify them when you call <a href=\"/en-US/docs/Web/API/MediaDevices/getUserMedia\" title=\"getUserMedia()\"><code>getUserMedia()</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>navigator.mediaDevices\n .getUserMedia({\n video: {\n width: { min: 640, ideal: 1920 },\n height: { min: 400, ideal: 1080 },\n aspectRatio: { ideal: 1.7777777778 },\n },\n audio: {\n sampleSize: 16,\n channelCount: 2,\n },\n })\n .then((stream) => {\n videoElement.srcObject = stream;\n })\n .catch(handleError);\n</code></pre></div>\n<p>In this example, constraints are applied at <code>getUserMedia()</code> time, asking for an ideal set of options with fallbacks for the video.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> You can specify one or more media input device IDs to establish restrictions on which input sources are allowed. To collect a list of the available devices, you can call <a href=\"/en-US/docs/Web/API/MediaDevices/enumerateDevices\" title=\"navigator.mediaDevices.enumerateDevices()\"><code>navigator.mediaDevices.enumerateDevices()</code></a>, then for each device which meets the desired criteria, add its <code>deviceId</code> to the <code>MediaConstraints</code> object that eventually gets passed into <code>getUserMedia()</code>.</p>\n</div>\n<p>You can also change the constraints of an existing <a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a> on the fly, by calling the track's <a href=\"/en-US/docs/Web/API/MediaStreamTrack/applyConstraints\" title=\"applyConstraints()\"><code>applyConstraints()</code></a> method, passing into it an object representing the constraints you wish to apply to the track:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>videoTrack.applyConstraints({\n width: 1920,\n height: 1080,\n});\n</code></pre></div>\n<p>In this snippet, the video track referenced by <code>videoTrack</code> is updated so that its resolution as closely as possible matches 1920x1080 pixels (1080p high definition).</p>"}},{"type":"prose","value":{"id":"retrieving_current_constraints_and_settings","title":"Retrieving current constraints and settings","isH3":false,"content":"<p>It's important to remember the difference between <strong>constraints</strong> and <strong>settings</strong>. Constraints are a way to specify what values you need, want, and are willing to accept for the various constrainable properties (as described in the documentation for <a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a>), while settings are the actual values of each constrainable property at the current time.</p>"}},{"type":"prose","value":{"id":"getting_the_constraints_in_effect","title":"Getting the constraints in effect","isH3":true,"content":"<p>If at any time you need to fetch the set of constraints that are currently applied to the media, you can get that information by calling <a href=\"/en-US/docs/Web/API/MediaStreamTrack/getConstraints\"><code>MediaStreamTrack.getConstraints()</code></a>, as shown in the example below.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function switchCameras(track, camera) {\n const constraints = track.getConstraints();\n constraints.facingMode = camera;\n track.applyConstraints(constraints);\n}\n</code></pre></div>\n<p>This function accepts a <a href=\"/en-US/docs/Web/API/MediaStreamTrack\"><code>MediaStreamTrack</code></a> and a string indicating the camera facing mode to use, fetches the current constraints, sets the value of the <a href=\"/en-US/docs/Web/API/MediaTrackConstraints/facingMode\"><code>MediaTrackConstraints.facingMode</code></a> to the specified value, then applies the updated constraint set.</p>"}},{"type":"prose","value":{"id":"getting_the_current_settings_for_a_track","title":"Getting the current settings for a track","isH3":true,"content":"<p>Unless you only use exact constraints (which is pretty restrictive, so be sure you mean it!), there's no guarantee exactly what you're going to actually get after the constraints are applied. The values of the constrainable properties as they actually are in the resulting media are referred to as the settings. If you need to know the true format and other properties of the media, you can obtain those settings by calling <a href=\"/en-US/docs/Web/API/MediaStreamTrack/getSettings\"><code>MediaStreamTrack.getSettings()</code></a>. This returns an object based on the dictionary <a href=\"/en-US/docs/Web/API/MediaTrackSettings\"><code>MediaTrackSettings</code></a>. For example:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function whichCamera(track) {\n return track.getSettings().facingMode;\n}\n</code></pre></div>\n<p>This function uses <code>getSettings()</code> to obtain the track's currently in-use values for the constrainable properties and returns the value of <a href=\"/en-US/docs/Web/API/MediaTrackSettings/facingMode\" title=\"facingMode\"><code>facingMode</code></a>.</p>"}},{"type":"prose","value":{"id":"example_constraint_exerciser","title":"Example: Constraint exerciser","isH3":false,"content":"<p>In this example, we create an exerciser which lets you experiment with media constraints by editing the source code describing the constraint sets for audio and video tracks. You can then apply those changes and see the result, including both what the stream looks like and what the actual media settings are set to after applying the new constraints.</p>\n<p>The HTML and CSS for this example are pretty simple, and aren't shown here. You can look at the complete example by <a href=\"#livesample_fullscreen=example_constraint_exerciser\">clicking here</a>.</p>\n<div class=\"code-example\"><pre class=\"brush: html hidden notranslate\"><code><p>\n Experiment with media constraints! Edit the constraint sets for the video and\n audio tracks in the edit boxes on the left, then click the \"Apply Constraints\"\n button to try them out. The actual settings the browser selected and is using\n are shown in the boxes on the right. Below all of that, you'll see the video\n itself.\n</p>\n<p>Click the \"Start\" button to begin.</p>\n\n<h3>Constrainable properties available:</h3>\n<ul id=\"supportedConstraints\"></ul>\n<div id=\"startButton\" class=\"button\">Start</div>\n<div class=\"wrapper\">\n <div class=\"track-row\">\n <div class=\"left-side\">\n <h3>Requested video constraints:</h3>\n <textarea id=\"videoConstraintEditor\" cols=\"32\" rows=\"8\"></textarea>\n </div>\n <div class=\"right-side\">\n <h3>Actual video settings:</h3>\n <textarea id=\"videoSettingsText\" cols=\"32\" rows=\"8\" disabled></textarea>\n </div>\n </div>\n <div class=\"track-row\">\n <div class=\"left-side\">\n <h3>Requested audio constraints:</h3>\n <textarea id=\"audioConstraintEditor\" cols=\"32\" rows=\"8\"></textarea>\n </div>\n <div class=\"right-side\">\n <h3>Actual audio settings:</h3>\n <textarea id=\"audioSettingsText\" cols=\"32\" rows=\"8\" disabled></textarea>\n </div>\n </div>\n\n <div class=\"button\" id=\"applyButton\">Apply Constraints</div>\n</div>\n<video id=\"video\" autoplay></video>\n\n<div class=\"button\" id=\"stopButton\">Stop Video</div>\n\n<div id=\"log\"></div>\n</code></pre></div>\n<div class=\"code-example\"><pre class=\"brush: css hidden notranslate\"><code>body {\n font:\n 14px \"Open Sans\",\n \"Arial\",\n sans-serif;\n}\n\nvideo {\n margin-top: 20px;\n border: 1px solid black;\n}\n\n.button {\n cursor: pointer;\n width: 150px;\n border: 1px solid black;\n font-size: 16px;\n text-align: center;\n padding-top: 2px;\n padding-bottom: 4px;\n color: white;\n background-color: darkgreen;\n}\n\n.wrapper {\n margin-bottom: 10px;\n width: 600px;\n}\n\n.track-row {\n height: 200px;\n}\n\n.left-side {\n float: left;\n width: calc(calc(100% / 2) - 10px);\n}\n\n.right-side {\n float: right;\n width: calc(calc(100% / 2) - 10px);\n}\n\ntextarea {\n padding: 8px;\n}\n\nh3 {\n margin-bottom: 3px;\n}\n\n#supportedConstraints {\n column-count: 2;\n}\n\n#log {\n padding-top: 10px;\n}\n</code></pre></div>"}},{"type":"prose","value":{"id":"defaults_and_variables","title":"Defaults and variables","isH3":true,"content":"<p>First we have the default constraint sets, as strings. These strings are presented in editable <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a>s, but this is the initial configuration of the stream.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const videoDefaultConstraintString =\n '{\\n \"width\": 320,\\n \"height\": 240,\\n \"frameRate\": 30\\n}';\nconst audioDefaultConstraintString =\n '{\\n \"sampleSize\": 16,\\n \"channelCount\": 2,\\n \"echoCancellation\": false\\n}';\n</code></pre></div>\n<p>These defaults ask for a pretty common camera configuration, but don't insist on any property being of special importance. The browser should do its best to match these settings but will settle for anything it considers a close match.</p>\n<p>Then we initialize the variables which will hold the <a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a> objects for the video and audio tracks, as well as the variables which will hold references to the video and audio tracks themselves, to <code>null</code>.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>let videoConstraints = null;\nlet audioConstraints = null;\n\nlet audioTrack = null;\nlet videoTrack = null;\n</code></pre></div>\n<p>And we get references to all of the elements we'll need to access.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const videoElement = document.getElementById(\"video\");\nconst logElement = document.getElementById(\"log\");\nconst supportedConstraintList = document.getElementById(\"supportedConstraints\");\nconst videoConstraintEditor = document.getElementById(\"videoConstraintEditor\");\nconst audioConstraintEditor = document.getElementById(\"audioConstraintEditor\");\nconst videoSettingsText = document.getElementById(\"videoSettingsText\");\nconst audioSettingsText = document.getElementById(\"audioSettingsText\");\n</code></pre></div>\n<p>These elements are:</p>\n<dl>\n <dt id=\"videoelement\"><a href=\"#videoelement\"><code>videoElement</code></a></dt>\n <dd>\n <p>The <a href=\"/en-US/docs/Web/HTML/Element/video\"><code><video></code></a> element that will show the stream.</p>\n </dd>\n <dt id=\"logelement\"><a href=\"#logelement\"><code>logElement</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/div\"><code><div></code></a> into which any error messages or other log-type output will be written.</p>\n </dd>\n <dt id=\"supportedconstraintlist\"><a href=\"#supportedconstraintlist\"><code>supportedConstraintList</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/ul\"><code><ul></code></a> (unordered list) into which we programmatically add the names of each of the constrainable properties supported by the user's browser.</p>\n </dd>\n <dt id=\"videoconstrainteditor\"><a href=\"#videoconstrainteditor\"><code>videoConstraintEditor</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a> element that lets the user edit the code for the video track's constraint set.</p>\n </dd>\n <dt id=\"audioconstrainteditor\"><a href=\"#audioconstrainteditor\"><code>audioConstraintEditor</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a> element that lets the user edit the code for the audio track's constraint set.</p>\n </dd>\n <dt id=\"videosettingstext\"><a href=\"#videosettingstext\"><code>videoSettingsText</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a> (which is always disabled) that displays the current settings for the video track's constrainable properties.</p>\n </dd>\n <dt id=\"audiosettingstext\"><a href=\"#audiosettingstext\"><code>audioSettingsText</code></a></dt>\n <dd>\n <p>A <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a> (which is always disabled) that displays the current settings for the audio track's constrainable properties.</p>\n </dd>\n</dl>\n<p>Finally, we set the current contents of the two constraint set editor elements to the defaults.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>videoConstraintEditor.value = videoDefaultConstraintString;\naudioConstraintEditor.value = audioDefaultConstraintString;\n</code></pre></div>"}},{"type":"prose","value":{"id":"updating_the_settings_display","title":"Updating the settings display","isH3":true,"content":"<p>To the right of each of the constraint set editors is a second text box which we use to display the current configuration of the track's configurable properties. This display is updated by the function <code>getCurrentSettings()</code>, which gets the current settings for the audio and video tracks and inserts the corresponding code into the tracks' settings display boxes by setting their <a href=\"/en-US/docs/Web/API/HTMLTextAreaElement/value\"><code>value</code></a>.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function getCurrentSettings() {\n if (videoTrack) {\n videoSettingsText.value = JSON.stringify(videoTrack.getSettings(), null, 2);\n }\n\n if (audioTrack) {\n audioSettingsText.value = JSON.stringify(audioTrack.getSettings(), null, 2);\n }\n}\n</code></pre></div>\n<p>This gets called after the stream first starts up, as well as any time we've applied updated constraints, as you'll see below.</p>"}},{"type":"prose","value":{"id":"building_the_track_constraint_set_objects","title":"Building the track constraint set objects","isH3":true,"content":"<p>The <code>buildConstraints()</code> function builds the <a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a> objects for the audio and video tracks using the code in the two tracks' constraint set edit boxes.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function buildConstraints() {\n try {\n videoConstraints = JSON.parse(videoConstraintEditor.value);\n audioConstraints = JSON.parse(audioConstraintEditor.value);\n } catch (error) {\n handleError(error);\n }\n}\n</code></pre></div>\n<p>This uses <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse\"><code>JSON.parse()</code></a> to parse the code in each editor into an object. If either call to JSON.parse() throws an exception, <code>handleError()</code> is called to output the error message to the log.</p>"}},{"type":"prose","value":{"id":"configuring_and_starting_the_stream","title":"Configuring and starting the stream","isH3":true,"content":"<p>The <code>startVideo()</code> method handles setting up and starting the video stream.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function startVideo() {\n buildConstraints();\n\n navigator.mediaDevices\n .getUserMedia({\n video: videoConstraints,\n audio: audioConstraints,\n })\n .then((stream) => {\n const audioTracks = stream.getAudioTracks();\n const videoTracks = stream.getVideoTracks();\n\n videoElement.srcObject = stream;\n\n if (audioTracks.length > 0) {\n audioTrack = audioTracks[0];\n }\n\n if (videoTracks.length > 0) {\n videoTrack = videoTracks[0];\n }\n })\n .then(() => {\n return new Promise((resolve) => {\n videoElement.onloadedmetadata = resolve;\n });\n })\n .then(() => {\n getCurrentSettings();\n })\n .catch(handleError);\n}\n</code></pre></div>\n<p>There are several steps here:</p>\n<ol>\n <li>It calls <code>buildConstraints()</code> to create the <a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a> objects for the two tracks from the code in the edit boxes.</li>\n <li>It calls <a href=\"/en-US/docs/Web/API/MediaDevices/getUserMedia\" title=\"navigator.mediaDevices.getUserMedia()\"><code>navigator.mediaDevices.getUserMedia()</code></a>, passing in the constraints objects for the video and audio tracks. This returns a <a href=\"/en-US/docs/Web/API/MediaStream\"><code>MediaStream</code></a> with the audio and video from a source matching the inputs (typically a webcam, although if you provide the right constraints you can get media from other sources).</li>\n <li>When the stream is obtained, it's attached to the <a href=\"/en-US/docs/Web/HTML/Element/video\"><code><video></code></a> element so that it's visible on screen, and we grab the audio track and video track into the variables <code>audioTrack</code> and <code>videoTrack</code>.</li>\n <li>Then we set up a promise which resolves when the <a href=\"/en-US/docs/Web/API/HTMLMediaElement/loadedmetadata_event\" title=\"loadedmetadata\"><code>loadedmetadata</code></a> event occurs on the video element.</li>\n <li>When that happens, we know the video has started playing, so we call our <code>getCurrentSettings()</code> function (described above) to display the actual settings that the browser decided upon after considering our constraints and the capabilities of the hardware.</li>\n <li>If an error occurs, we log it using the <code>handleError()</code> method that we'll look at farther down in this article.</li>\n</ol>\n<p>We also need to set up an event listener to watch for the \"Start Video\" button to be clicked:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>document.getElementById(\"startButton\").addEventListener(\n \"click\",\n () => {\n startVideo();\n },\n false,\n);\n</code></pre></div>"}},{"type":"prose","value":{"id":"applying_constraint_set_updates","title":"Applying constraint set updates","isH3":true,"content":"<p>Next, we set up an event listener for the \"Apply Constraints\" button. If it's clicked and there's not already media in use, we call <code>startVideo()</code>, and let that function handle starting the stream with the specified settings in place. Otherwise, we follow these steps to apply the updated constraints to the already-active stream:</p>\n<ol>\n <li><code>buildConstraints()</code> is called to construct updated <a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a> objects for the audio track (<code>audioConstraints</code>) and the video track (<code>videoConstraints</code>).</li>\n <li><a href=\"/en-US/docs/Web/API/MediaStreamTrack/applyConstraints\"><code>MediaStreamTrack.applyConstraints()</code></a> is called on the video track (if there is one) to apply the new <code>videoConstraints</code>. If this succeeds, the contents of the video track's current settings box are updated based on the result of calling its <a href=\"/en-US/docs/Web/API/MediaStreamTrack/getSettings\" title=\"getSettings()\"><code>getSettings()</code></a> method.</li>\n <li>Once that's done, <code>applyConstraints()</code> is called on the audio track (if there is one) to apply the new audio constraints. If this succeeds, the contents of the audio track's current settings box are updated based on the result of calling its <a href=\"/en-US/docs/Web/API/MediaStreamTrack/getSettings\" title=\"getSettings()\"><code>getSettings()</code></a> method.</li>\n <li>If an error occurs applying either set of constraints, <code>handleError()</code> is used to output a message into the log.</li>\n</ol>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>document.getElementById(\"applyButton\").addEventListener(\n \"click\",\n () => {\n if (!videoTrack && !audioTrack) {\n startVideo();\n } else {\n buildConstraints();\n\n const prettyJson = (obj) => JSON.stringify(obj, null, 2);\n\n if (videoTrack) {\n videoTrack\n .applyConstraints(videoConstraints)\n .then(() => {\n videoSettingsText.value = prettyJson(videoTrack.getSettings());\n })\n .catch(handleError);\n }\n\n if (audioTrack) {\n audioTrack\n .applyConstraints(audioConstraints)\n .then(() => {\n audioSettingsText.value = prettyJson(audioTrack.getSettings());\n })\n .catch(handleError);\n }\n }\n },\n false,\n);\n</code></pre></div>"}},{"type":"prose","value":{"id":"handling_the_stop_button","title":"Handling the stop button","isH3":true,"content":"<p>Then we set up the handler for the stop button.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>document.getElementById(\"stopButton\").addEventListener(\"click\", () => {\n if (videoTrack) {\n videoTrack.stop();\n }\n\n if (audioTrack) {\n audioTrack.stop();\n }\n\n videoTrack = audioTrack = null;\n videoElement.srcObject = null;\n});\n</code></pre></div>\n<p>This stops the active tracks, sets the <code>videoTrack</code> and <code>audioTrack</code> variables to <code>null</code> so we know they're gone, and removes the stream from the <a href=\"/en-US/docs/Web/HTML/Element/video\"><code><video></code></a> element by setting <a href=\"/en-US/docs/Web/API/HTMLMediaElement/srcObject\"><code>HTMLMediaElement.srcObject</code></a> to <code>null</code>.</p>"}},{"type":"prose","value":{"id":"simple_tab_support_in_the_editor","title":"Simple tab support in the editor","isH3":true,"content":"<p>This code adds simple support for tabs to the <a href=\"/en-US/docs/Web/HTML/Element/textarea\"><code><textarea></code></a> elements by making the tab key insert two space characters when either constraint edit box is focused.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function keyDownHandler(event) {\n if (event.key === \"Tab\") {\n const elem = event.target;\n const str = elem.value;\n\n const position = elem.selectionStart;\n const beforeTab = str.substring(0, position);\n const afterTab = str.substring(position, str.length);\n const newStr = `${beforeTab} ${afterTab}`;\n elem.value = newStr;\n elem.selectionStart = elem.selectionEnd = position + 2;\n event.preventDefault();\n }\n}\n\nvideoConstraintEditor.addEventListener(\"keydown\", keyDownHandler, false);\naudioConstraintEditor.addEventListener(\"keydown\", keyDownHandler, false);\n</code></pre></div>"}},{"type":"prose","value":{"id":"show_constrainable_properties_the_browser_supports","title":"Show constrainable properties the browser supports","isH3":true,"content":"<p>The last significant piece of the puzzle: code that displays, for the user's reference, a list of the constrainable properties which their browser supports. Each property is a link to its documentation on MDN for the user's convenience. See the <a href=\"/en-US/docs/Web/API/MediaDevices/getSupportedConstraints#examples\"><code>MediaDevices.getSupportedConstraints()</code> examples</a> for details on how this code works.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> Of course, there may be non-standard properties in this list, in which case you probably will find that the documentation link doesn't help much.</p>\n</div>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const supportedConstraints = navigator.mediaDevices.getSupportedConstraints();\nfor (const constraint in supportedConstraints) {\n if (Object.hasOwn(supportedConstraints, constraint)) {\n const elem = document.createElement(\"li\");\n\n elem.innerHTML = `<code><a href='https://developer.mozilla.org/docs/Web/API/MediaTrackSupportedConstraints/${constraint}' target='_blank'>${constraint}</a></code>`;\n supportedConstraintList.appendChild(elem);\n }\n}\n</code></pre></div>"}},{"type":"prose","value":{"id":"error_handling","title":"Error handling","isH3":true,"content":"<p>We also have some simple error handling code; <code>handleError()</code> is called to handle promises which fail, and the <code>log()</code> function appends the error message to a special logging <a href=\"/en-US/docs/Web/HTML/Element/div\"><code><div></code></a> box under the video.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function log(msg) {\n logElement.innerHTML += `${msg}<br>`;\n}\n\nfunction handleError(reason) {\n log(\n `Error <code>${reason.name}</code> in constraint <code>${reason.constraint}</code>: ${reason.message}`,\n );\n}\n</code></pre></div>"}},{"type":"prose","value":{"id":"result","title":"Result","isH3":true,"content":"<p>Here you can see the complete example in action.</p><div class=\"code-example\"><div class=\"example-header\"></div><iframe class=\"sample-code-frame\" title=\"Example Constraint exerciser sample\" id=\"frame_example_constraint_exerciser\" width=\"650\" height=\"800\" src=\"about:blank\" data-live-path=\"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints\" data-live-id=\"example_constraint_exerciser\" sandbox=\"allow-same-origin allow-scripts\" loading=\"lazy\"></iframe></div>"}},{"type":"specifications","value":{"title":"Specifications","id":"specifications","isH3":false,"specifications":[{"bcdSpecificationURL":"https://w3c.github.io/mediacapture-main/#dom-mediadevices-getsupportedconstraints","title":"Media Capture and Streams"}],"query":"api.MediaDevices.getSupportedConstraints"}},{"type":"browser_compatibility","value":{"title":"Browser compatibility","id":"browser_compatibility","isH3":false,"query":"api.MediaDevices.getSupportedConstraints"}},{"type":"prose","value":{"id":"see_also","title":"See also","isH3":false,"content":"<ul>\n <li><a href=\"/en-US/docs/Web/API/Media_Capture_and_Streams_API\">Media Capture and Streams API</a></li>\n <li><a href=\"/en-US/docs/Web/API/MediaTrackConstraints\"><code>MediaTrackConstraints</code></a></li>\n <li><a href=\"/en-US/docs/Web/API/MediaTrackSettings\"><code>MediaTrackSettings</code></a></li>\n <li><a href=\"/en-US/docs/Web/API/MediaDevices/getSupportedConstraints\"><code>MediaDevices.getSupportedConstraints()</code></a></li>\n <li><a href=\"/en-US/docs/Web/API/MediaStreamTrack/applyConstraints\"><code>MediaStreamTrack.applyConstraints()</code></a></li>\n <li><a href=\"/en-US/docs/Web/API/MediaStreamTrack/getSettings\"><code>MediaStreamTrack.getSettings()</code></a></li>\n</ul>"}}],"toc":[{"text":"Overview","id":"overview"},{"text":"Determining if a constraint is supported","id":"determining_if_a_constraint_is_supported"},{"text":"How constraints are defined","id":"how_constraints_are_defined"},{"text":"Checking capabilities","id":"checking_capabilities"},{"text":"Applying constraints","id":"applying_constraints"},{"text":"Retrieving current constraints and settings","id":"retrieving_current_constraints_and_settings"},{"text":"Example: Constraint exerciser","id":"example_constraint_exerciser"},{"text":"Specifications","id":"specifications"},{"text":"Browser compatibility","id":"browser_compatibility"},{"text":"See also","id":"see_also"}],"summary":"This article discusses the twin concepts of constraints and capabilities, as well as media settings, and includes an example we call the Constraint Exerciser. The Constraint Exerciser lets you experiment with the results of different constraint sets being applied to the audio and video tracks coming from the computer's A/V input devices (such as its webcam and microphone).","popularity":0.0117,"modified":"2024-10-27T23:53:01.000Z","other_translations":[{"locale":"de","title":"Fähigkeiten, Einschränkungen und Einstellungen","native":"Deutsch"},{"locale":"ja","title":"能力と制約と設定","native":"日本語"}],"pageType":"guide","source":{"folder":"en-us/web/api/media_capture_and_streams_api/constraints","github_url":"https://github.com/mdn/content/blob/main/files/en-us/web/api/media_capture_and_streams_api/constraints/index.md","last_commit_url":"https://github.com/mdn/content/commit/bff3a6a2e6b3c13dd8bb0c80a1eb9da08cce5dc6","filename":"index.md"},"short_title":"Capabilities, constraints, and settings","parents":[{"uri":"/en-US/docs/Web","title":"References"},{"uri":"/en-US/docs/Web/API","title":"Web APIs"},{"uri":"/en-US/docs/Web/API/Media_Capture_and_Streams_API","title":"Media Capture and Streams API (Media Stream)"},{"uri":"/en-US/docs/Web/API/Media_Capture_and_Streams_API/Constraints","title":"Capabilities, constraints, and settings"}],"pageTitle":"Capabilities, constraints, and settings - Web APIs | MDN","noIndexing":false}}</script></body></html>