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index.html
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<!doctype html><html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>HTMLVideoElement.requestVideoFrameCallback()</title>
<meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
<link href="https://www.w3.org/StyleSheets/TR/2021/cg-draft" rel="stylesheet">
<meta content="Bikeshed version c3a8ac783, updated Wed Jul 24 12:20:06 2024 -0700" name="generator">
<link href="https://wicg.github.io/video-rvfc/" rel="canonical">
<meta content="581d7d45aa3f43e6e1fed4d3f22a753e6a43b103" name="revision">
<meta content="dark light" name="color-scheme">
<link href="https://www.w3.org/StyleSheets/TR/2021/dark.css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css">
<style>/* Boilerplate: style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
color: var(--a-normal-text);
font-size: inherit;
font-family: inherit;
}
.css::before, .property::before, .descriptor::before {
content: "‘";
}
.css::after, .property::after, .descriptor::after {
content: "’";
}
.property, .descriptor {
/* Don't wrap property and descriptor names */
white-space: nowrap;
}
.type { /* CSS value <type> */
font-style: italic;
}
pre .property::before, pre .property::after {
content: "";
}
[data-link-type="property"]::before,
[data-link-type="propdesc"]::before,
[data-link-type="descriptor"]::before,
[data-link-type="value"]::before,
[data-link-type="function"]::before,
[data-link-type="at-rule"]::before,
[data-link-type="selector"]::before,
[data-link-type="maybe"]::before {
content: "‘";
}
[data-link-type="property"]::after,
[data-link-type="propdesc"]::after,
[data-link-type="descriptor"]::after,
[data-link-type="value"]::after,
[data-link-type="function"]::after,
[data-link-type="at-rule"]::after,
[data-link-type="selector"]::after,
[data-link-type="maybe"]::after {
content: "’";
}
[data-link-type].production::before,
[data-link-type].production::after,
.prod [data-link-type]::before,
.prod [data-link-type]::after {
content: "";
}
[data-link-type=element],
[data-link-type=element-attr] {
font-family: Menlo, Consolas, "DejaVu Sans Mono", monospace;
font-size: .9em;
}
[data-link-type=element]::before { content: "<" }
[data-link-type=element]::after { content: ">" }
[data-link-type=biblio] {
white-space: pre;
}
@media (prefers-color-scheme: dark) {
:root {
--selflink-text: black;
--selflink-bg: silver;
--selflink-hover-text: white;
}
}
</style>
<style>/* Boilerplate: style-colors */
/* Any --*-text not paired with a --*-bg is assumed to have a transparent bg */
:root {
color-scheme: light dark;
--text: black;
--bg: white;
--unofficial-watermark: url(https://www.w3.org/StyleSheets/TR/2016/logos/UD-watermark);
--logo-bg: #1a5e9a;
--logo-active-bg: #c00;
--logo-text: white;
--tocnav-normal-text: #707070;
--tocnav-normal-bg: var(--bg);
--tocnav-hover-text: var(--tocnav-normal-text);
--tocnav-hover-bg: #f8f8f8;
--tocnav-active-text: #c00;
--tocnav-active-bg: var(--tocnav-normal-bg);
--tocsidebar-text: var(--text);
--tocsidebar-bg: #f7f8f9;
--tocsidebar-shadow: rgba(0,0,0,.1);
--tocsidebar-heading-text: hsla(203,20%,40%,.7);
--toclink-text: var(--text);
--toclink-underline: #3980b5;
--toclink-visited-text: var(--toclink-text);
--toclink-visited-underline: #054572;
--heading-text: #005a9c;
--hr-text: var(--text);
--algo-border: #def;
--del-text: red;
--del-bg: transparent;
--ins-text: #080;
--ins-bg: transparent;
--a-normal-text: #034575;
--a-normal-underline: #bbb;
--a-visited-text: var(--a-normal-text);
--a-visited-underline: #707070;
--a-hover-bg: rgba(75%, 75%, 75%, .25);
--a-active-text: #c00;
--a-active-underline: #c00;
--blockquote-border: silver;
--blockquote-bg: transparent;
--blockquote-text: currentcolor;
--issue-border: #e05252;
--issue-bg: #fbe9e9;
--issue-text: var(--text);
--issueheading-text: #831616;
--example-border: #e0cb52;
--example-bg: #fcfaee;
--example-text: var(--text);
--exampleheading-text: #574b0f;
--note-border: #52e052;
--note-bg: #e9fbe9;
--note-text: var(--text);
--noteheading-text: hsl(120, 70%, 30%);
--notesummary-underline: silver;
--assertion-border: #aaa;
--assertion-bg: #eee;
--assertion-text: black;
--advisement-border: orange;
--advisement-bg: #fec;
--advisement-text: var(--text);
--advisementheading-text: #b35f00;
--warning-border: red;
--warning-bg: hsla(40,100%,50%,0.95);
--warning-text: var(--text);
--amendment-border: #330099;
--amendment-bg: #F5F0FF;
--amendment-text: var(--text);
--amendmentheading-text: #220066;
--def-border: #8ccbf2;
--def-bg: #def;
--def-text: var(--text);
--defrow-border: #bbd7e9;
--datacell-border: silver;
--indexinfo-text: #707070;
--indextable-hover-text: black;
--indextable-hover-bg: #f7f8f9;
--outdatedspec-bg: rgba(0, 0, 0, .5);
--outdatedspec-text: black;
--outdated-bg: maroon;
--outdated-text: white;
--outdated-shadow: red;
--editedrec-bg: darkorange;
}
@media (prefers-color-scheme: dark) {
:root {
--text: #ddd;
--bg: black;
--unofficial-watermark: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400'%3E%3Cg fill='%23100808' transform='translate(200 200) rotate(-45) translate(-200 -200)' stroke='%23100808' stroke-width='3'%3E%3Ctext x='50%25' y='220' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EUNOFFICIAL%3C/text%3E%3Ctext x='50%25' y='305' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EDRAFT%3C/text%3E%3C/g%3E%3C/svg%3E");
--logo-bg: #1a5e9a;
--logo-active-bg: #c00;
--logo-text: white;
--tocnav-normal-text: #999;
--tocnav-normal-bg: var(--bg);
--tocnav-hover-text: var(--tocnav-normal-text);
--tocnav-hover-bg: #080808;
--tocnav-active-text: #f44;
--tocnav-active-bg: var(--tocnav-normal-bg);
--tocsidebar-text: var(--text);
--tocsidebar-bg: #080808;
--tocsidebar-shadow: rgba(255,255,255,.1);
--tocsidebar-heading-text: hsla(203,20%,40%,.7);
--toclink-text: var(--text);
--toclink-underline: #6af;
--toclink-visited-text: var(--toclink-text);
--toclink-visited-underline: #054572;
--heading-text: #8af;
--hr-text: var(--text);
--algo-border: #456;
--del-text: #f44;
--del-bg: transparent;
--ins-text: #4a4;
--ins-bg: transparent;
--a-normal-text: #6af;
--a-normal-underline: #555;
--a-visited-text: var(--a-normal-text);
--a-visited-underline: var(--a-normal-underline);
--a-hover-bg: rgba(25%, 25%, 25%, .2);
--a-active-text: #f44;
--a-active-underline: var(--a-active-text);
--borderedblock-bg: rgba(255, 255, 255, .05);
--blockquote-border: silver;
--blockquote-bg: var(--borderedblock-bg);
--blockquote-text: currentcolor;
--issue-border: #e05252;
--issue-bg: var(--borderedblock-bg);
--issue-text: var(--text);
--issueheading-text: hsl(0deg, 70%, 70%);
--example-border: hsl(50deg, 90%, 60%);
--example-bg: var(--borderedblock-bg);
--example-text: var(--text);
--exampleheading-text: hsl(50deg, 70%, 70%);
--note-border: hsl(120deg, 100%, 35%);
--note-bg: var(--borderedblock-bg);
--note-text: var(--text);
--noteheading-text: hsl(120, 70%, 70%);
--notesummary-underline: silver;
--assertion-border: #444;
--assertion-bg: var(--borderedblock-bg);
--assertion-text: var(--text);
--advisement-border: orange;
--advisement-bg: #222218;
--advisement-text: var(--text);
--advisementheading-text: #f84;
--warning-border: red;
--warning-bg: hsla(40,100%,20%,0.95);
--warning-text: var(--text);
--amendment-border: #330099;
--amendment-bg: #080010;
--amendment-text: var(--text);
--amendmentheading-text: #cc00ff;
--def-border: #8ccbf2;
--def-bg: #080818;
--def-text: var(--text);
--defrow-border: #136;
--datacell-border: silver;
--indexinfo-text: #aaa;
--indextable-hover-text: var(--text);
--indextable-hover-bg: #181818;
--outdatedspec-bg: rgba(255, 255, 255, .5);
--outdatedspec-text: black;
--outdated-bg: maroon;
--outdated-text: white;
--outdated-shadow: red;
--editedrec-bg: darkorange;
}
/* In case a transparent-bg image doesn't expect to be on a dark bg,
which is quite common in practice... */
img { background: white; }
}
</style>
<style>/* Boilerplate: style-counters */
body {
counter-reset: example figure issue;
}
.issue {
counter-increment: issue;
}
.issue:not(.no-marker)::before {
content: "Issue " counter(issue);
}
.example {
counter-increment: example;
}
.example:not(.no-marker)::before {
content: "Example " counter(example);
}
.invalid.example:not(.no-marker)::before,
.illegal.example:not(.no-marker)::before {
content: "Invalid Example" counter(example);
}
figcaption {
counter-increment: figure;
}
figcaption:not(.no-marker)::before {
content: "Figure " counter(figure) " ";
}
</style>
<style>/* Boilerplate: style-dfn-panel */
:root {
--dfnpanel-bg: #ddd;
--dfnpanel-text: var(--text);
--dfnpanel-target-bg: #ffc;
--dfnpanel-target-outline: orange;
}
@media (prefers-color-scheme: dark) {
:root {
--dfnpanel-bg: #222;
--dfnpanel-text: var(--text);
--dfnpanel-target-bg: #333;
--dfnpanel-target-outline: silver;
}
}
.dfn-panel {
position: absolute;
z-index: 35;
width: 20em;
width: 300px;
height: auto;
max-height: 500px;
overflow: auto;
padding: 0.5em 0.75em;
font: small Helvetica Neue, sans-serif, Droid Sans Fallback;
background: var(--dfnpanel-bg);
color: var(--dfnpanel-text);
border: outset 0.2em;
white-space: normal; /* in case it's moved into a pre */
}
.dfn-panel:not(.on) { display: none; }
.dfn-panel * { margin: 0; padding: 0; text-indent: 0; }
.dfn-panel > b { display: block; }
.dfn-panel a { color: var(--dfnpanel-text); }
.dfn-panel a:not(:hover) { text-decoration: none !important; border-bottom: none !important; }
.dfn-panel a:focus {
outline: 5px auto Highlight;
outline: 5px auto -webkit-focus-ring-color;
}
.dfn-panel > b + b { margin-top: 0.25em; }
.dfn-panel ul { padding: 0 0 0 1em; list-style: none; }
.dfn-panel li a {
max-width: calc(300px - 1.5em - 1em);
overflow: hidden;
text-overflow: ellipsis;
}
.dfn-panel.activated {
display: inline-block;
position: fixed;
left: 8px;
bottom: 2em;
margin: 0 auto;
max-width: calc(100vw - 1.5em - .4em - .5em);
max-height: 30vh;
transition: left 1s ease-out, bottom 1s ease-out;
}
.dfn-panel .link-item:hover {
text-decoration: underline;
}
.dfn-panel .link-item .copy-icon {
opacity: 0;
}
.dfn-panel .link-item:hover .copy-icon,
.dfn-panel .link-item .copy-icon:focus {
opacity: 1;
}
.dfn-panel .copy-icon {
display: inline-block;
margin-right: 0.5em;
width: 0.85em;
height: 1em;
border-radius: 3px;
background-color: #ccc;
cursor: pointer;
}
.dfn-panel .copy-icon .icon {
width: 100%;
height: 100%;
background-color: #fff;
display: flex;
justify-content: center;
align-items: center;
position: relative;
}
.dfn-panel .copy-icon .icon::before {
content: "";
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
border: 1px solid black;
background-color: #ccc;
opacity: 0.25;
transform: translate(3px, -3px);
}
.dfn-panel .copy-icon:active .icon::before {
opacity: 1;
}
.dfn-paneled[role="button"] { cursor: help; }
.highlighted {
animation: target-fade 3s;
}
@keyframes target-fade {
from {
background-color: var(--dfnpanel-target-bg);
outline: 5px solid var(--dfnpanel-target-outline);
}
to {
color: var(--a-normal-text);
background-color: transparent;
outline: transparent;
}
}
</style>
<style>/* Boilerplate: style-idl-highlighting */
pre.idl.highlight {
background: var(--borderedblock-bg, var(--def-bg));
}
</style>
<style>/* Boilerplate: style-issues */
a[href].issue-return {
float: right;
float: inline-end;
color: var(--issueheading-text);
font-weight: bold;
text-decoration: none;
}
</style>
<style>/* Boilerplate: style-md-lists */
/* This is a weird hack for me not yet following the commonmark spec
regarding paragraph and lists. */
[data-md] > :first-child {
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<p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width="72"> </a> </p>
<h1 class="p-name no-ref" id="title">HTMLVideoElement.requestVideoFrameCallback()</h1>
<p id="w3c-state"><a href="https://www.w3.org/standards/types#CG-DRAFT">Draft Community Group Report</a>, <time class="dt-updated" datetime="2024-08-02">2 August 2024</time></p>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="https://wicg.github.io/video-rvfc/">https://wicg.github.io/video-rvfc/</a>
<dt>Issue Tracking:
<dd><a href="https://github.com/wicg/video-rvfc/issues/">GitHub</a>
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editor:
<dd class="editor p-author h-card vcard" data-editor-id="120583"><span class="p-name fn">Thomas Guilbert</span> (<a class="p-org org" href="https://google.com/">Google Inc.</a>)
<dt>Participate:
<dd><a href="https://github.com/wicg/video-rvfc">Git Repository.</a>
<dd><a href="https://github.com/wicg/video-rvfc/issues/new">File an issue.</a>
<dt>Version History:
<dd><a href="https://github.com/wicg/video-rvfc/commits">https://github.com/wicg/video-rvfc/commits</a>
</dl>
</div>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/policies/#copyright">Copyright</a> © 2024 the Contributors to the HTMLVideoElement.requestVideoFrameCallback() Specification, published by the <a href="https://www.w3.org/community/wicg/">Web Platform Incubator Community Group</a> under the <a href="https://www.w3.org/community/about/agreements/cla/">W3C Community Contributor License Agreement (CLA)</a>.
A human-readable <a href="http://www.w3.org/community/about/agreements/cla-deed/">summary</a> is available. </p>
<hr title="Separator for header">
</div>
<div class="p-summary" data-fill-with="abstract">
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<p><video>.requestVideoFrameCallback() allows web authors to be notified when a frame has been presented for composition.</p>
</div>
<div data-fill-with="at-risk"></div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="status">
<p> This specification was published by the <a href="https://www.w3.org/community/wicg/">Web Platform Incubator Community Group</a>.
It is not a W3C Standard nor is it on the W3C Standards Track.
Please note that under the <a href="https://www.w3.org/community/about/agreements/cla/">W3C Community Contributor License Agreement (CLA)</a> there is a limited opt-out and other conditions apply.
Learn more about <a href="http://www.w3.org/community/">W3C Community and Business Groups</a>. </p>
<p></p>
</div>
<div data-fill-with="at-risk"></div>
<nav data-fill-with="table-of-contents" id="toc">
<h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
<ol class="toc" role="directory">
<li><a href="#introduction"><span class="secno">1</span> <span class="content">Introduction</span></a>
<li>
<a href="#video-frame-callback-metadata"><span class="secno">2</span> <span class="content">VideoFrameCallbackMetadata</span></a>
<ol class="toc">
<li><a href="#video-frame-callback-metadata-definitions"><span class="secno">2.1</span> <span class="content">Definitions</span></a>
<li><a href="#video-frame-callback-metadata-attributes"><span class="secno">2.2</span> <span class="content">Attributes</span></a>
</ol>
<li><a href="#video-frame-request-callback"><span class="secno">3</span> <span class="content">VideoFrameRequestCallback</span></a>
<li>
<a href="#video-rvfc"><span class="secno">4</span> <span class="content">HTMLVideoElement.requestVideoFrameCallback()</span></a>
<ol class="toc">
<li><a href="#video-rvfc-methods"><span class="secno">4.1</span> <span class="content">Methods</span></a>
<li><a href="#video-rvfc-procedures"><span class="secno">4.2</span> <span class="content">Procedures</span></a>
</ol>
<li><a href="#security-and-privacy"><span class="secno">5</span> <span class="content">Security and Privacy Considerations</span></a>
<li>
<a href="#examples"><span class="secno">6</span> <span class="content">Examples</span></a>
<ol class="toc">
<li><a href="#example-drawing"><span class="secno">6.1</span> <span class="content">Drawing frames at the video rate</span></a>
</ol>
<li>
<a href="#w3c-conformance"><span class="secno"></span> <span class="content">Conformance</span></a>
<ol class="toc">
<li><a href="#w3c-conventions"><span class="secno"></span> <span class="content">Document conventions</span></a>
</ol>
<li>
<a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ol class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ol>
<li>
<a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ol class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ol>
<li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
<li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
</ol>
</nav>
<main>
<h2 class="heading settled" data-level="1" id="introduction"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#introduction"></a></h2>
<p><em>This section is non-normative</em></p>
<p>This is a proposal to add a <code class="idl"><a data-link-type="idl" href="#dom-htmlvideoelement-requestvideoframecallback" id="ref-for-dom-htmlvideoelement-requestvideoframecallback">requestVideoFrameCallback()</a></code> method to the <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement">HTMLVideoElement</a></code>.</p>
<p>This method allows web authors to register a <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback">callback</a></code> which runs in the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering" id="ref-for-update-the-rendering">rendering steps</a>, when a new video frame is sent to the compositor. The
new <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback①">callbacks</a></code> are executed immediately before existing <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/imagebitmap-and-animations.html#animationframeprovider" id="ref-for-animationframeprovider">window.requestAnimationFrame()</a></code> callbacks. Changes made from within both
callback types within the same <a data-link-type="dfn">turn of the event loop</a> will be visible on
screen at the same time, with the next v-sync.</p>
<p>Drawing operations (e.g. drawing a video frame to a <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/imagebitmap-and-animations.html#canvas" id="ref-for-canvas">canvas</a></code> via <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-drawimage" id="ref-for-dom-context-2d-drawimage">drawImage()</a></code>) made through this
API will be synchronized as a <em>best effort</em> with the video playing on screen. <em>Best effort</em> in this case
means that, even with a normal work load, a <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback②">callback</a></code> can occasionally be
fired one v-sync late, relative to when the new video frame was presented. This means that drawing
operations might occasionally appear on screen one v-sync after the video frame does. Additionally, if
there is a heavy load on the main thread, we might not get a callback for every frame (as measured by a
discontinuity in the <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-presentedframes" id="ref-for-dom-videoframecallbackmetadata-presentedframes">presentedFrames</a></code>).</p>
<p class="note" role="note"><span class="marker">Note:</span> A web author could know if a callback is late by checking whether <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-expecteddisplaytime" id="ref-for-dom-videoframecallbackmetadata-expecteddisplaytime">expectedDisplayTime</a></code> is equal
to <em>now</em>, as opposed to roughly one v-sync in the future.</p>
<p>The <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback③">VideoFrameRequestCallback</a></code> also provides useful <code class="idl"><a data-link-type="idl" href="#dictdef-videoframecallbackmetadata" id="ref-for-dictdef-videoframecallbackmetadata">metadata</a></code> about the video
frame that was most recently presented for composition, which can be used for automated metrics analysis.</p>
<h2 class="heading settled" data-level="2" id="video-frame-callback-metadata"><span class="secno">2. </span><span class="content">VideoFrameCallbackMetadata</span><a class="self-link" href="#video-frame-callback-metadata"></a></h2>
<pre class="idl highlight def"><c- b>dictionary</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="dictionary" data-export id="dictdef-videoframecallbackmetadata"><code><c- g>VideoFrameCallbackMetadata</c-></code></dfn> {
<c- b>required</c-> <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp"><c- n>DOMHighResTimeStamp</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="DOMHighResTimeStamp" href="#dom-videoframecallbackmetadata-presentationtime" id="ref-for-dom-videoframecallbackmetadata-presentationtime"><c- g>presentationTime</c-></a>;
<c- b>required</c-> <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp①"><c- n>DOMHighResTimeStamp</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="DOMHighResTimeStamp" href="#dom-videoframecallbackmetadata-expecteddisplaytime" id="ref-for-dom-videoframecallbackmetadata-expecteddisplaytime①"><c- g>expectedDisplayTime</c-></a>;
<c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long"><c- b>unsigned</c-> <c- b>long</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="unsigned long" href="#dom-videoframecallbackmetadata-width" id="ref-for-dom-videoframecallbackmetadata-width"><c- g>width</c-></a>;
<c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long①"><c- b>unsigned</c-> <c- b>long</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="unsigned long" href="#dom-videoframecallbackmetadata-height" id="ref-for-dom-videoframecallbackmetadata-height"><c- g>height</c-></a>;
<c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-double" id="ref-for-idl-double"><c- b>double</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="double" href="#dom-videoframecallbackmetadata-mediatime" id="ref-for-dom-videoframecallbackmetadata-mediatime"><c- g>mediaTime</c-></a>;
<c- b>required</c-> <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long②"><c- b>unsigned</c-> <c- b>long</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="unsigned long" href="#dom-videoframecallbackmetadata-presentedframes" id="ref-for-dom-videoframecallbackmetadata-presentedframes①"><c- g>presentedFrames</c-></a>;
<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-double" id="ref-for-idl-double①"><c- b>double</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="double" href="#dom-videoframecallbackmetadata-processingduration" id="ref-for-dom-videoframecallbackmetadata-processingduration"><c- g>processingDuration</c-></a>;
<a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp②"><c- n>DOMHighResTimeStamp</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="DOMHighResTimeStamp" href="#dom-videoframecallbackmetadata-capturetime" id="ref-for-dom-videoframecallbackmetadata-capturetime"><c- g>captureTime</c-></a>;
<a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp③"><c- n>DOMHighResTimeStamp</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="DOMHighResTimeStamp" href="#dom-videoframecallbackmetadata-receivetime" id="ref-for-dom-videoframecallbackmetadata-receivetime"><c- g>receiveTime</c-></a>;
<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long③"><c- b>unsigned</c-> <c- b>long</c-></a> <a class="idl-code" data-link-type="dict-member" data-type="unsigned long" href="#dom-videoframecallbackmetadata-rtptimestamp" id="ref-for-dom-videoframecallbackmetadata-rtptimestamp"><c- g>rtpTimestamp</c-></a>;
};
</pre>
<h3 class="heading settled" data-level="2.1" id="video-frame-callback-metadata-definitions"><span class="secno">2.1. </span><span class="content">Definitions</span><a class="self-link" href="#video-frame-callback-metadata-definitions"></a></h3>
<p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="media-pixels">media pixels</dfn> are defined as a media resource’s visible decoded pixels, without pixel aspect
ratio adjustments. They are different from <a data-link-type="dfn" href="https://drafts.csswg.org/css-values/#px" id="ref-for-px">CSS pixels</a>, which account for pixel aspect ratio
adjustments.</p>
<h3 class="heading settled" data-level="2.2" id="video-frame-callback-metadata-attributes"><span class="secno">2.2. </span><span class="content">Attributes</span><a class="self-link" href="#video-frame-callback-metadata-attributes"></a></h3>
<dl>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-presentationtime"><code>presentationTime</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp④">DOMHighResTimeStamp</a></span>
<dd data-md>
<p>The time at which the user agent submitted the frame for composition.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-expecteddisplaytime"><code>expectedDisplayTime</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp⑤">DOMHighResTimeStamp</a></span>
<dd data-md>
<p>The time at which the user agent expects the frame to be visible.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-width"><code>width</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long④">unsigned long</a></span>
<dd data-md>
<p>The width of the video frame, in <a data-link-type="dfn" href="#media-pixels" id="ref-for-media-pixels">media pixels</a>.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-height"><code>height</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long⑤">unsigned long</a></span>
<dd data-md>
<p>The height of the video frame, in <a data-link-type="dfn" href="#media-pixels" id="ref-for-media-pixels①">media pixels</a>.</p>
</dl>
<p class="note" role="note"><span class="marker">Note:</span> <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-width" id="ref-for-dom-videoframecallbackmetadata-width①">width</a></code> and <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-height" id="ref-for-dom-videoframecallbackmetadata-height①">height</a></code> might differ from <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#dom-video-videowidth" id="ref-for-dom-video-videowidth">videoWidth</a></code> and <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#dom-video-videoheight" id="ref-for-dom-video-videoheight">videoHeight</a></code> in certain cases (e.g, an anamorphic video might
have rectangular pixels). When a calling <a href="https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/texImage2D"><code>texImage2D()</code></a>, <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-width" id="ref-for-dom-videoframecallbackmetadata-width②">width</a></code> and <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-height" id="ref-for-dom-videoframecallbackmetadata-height②">height</a></code> are the dimensions used to copy the video’s <a data-link-type="dfn" href="#media-pixels" id="ref-for-media-pixels②">media pixels</a> to the texture,
while <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#dom-video-videowidth" id="ref-for-dom-video-videowidth①">videoWidth</a></code> and <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#dom-video-videoheight" id="ref-for-dom-video-videoheight①">videoHeight</a></code> can
be used to determine the aspect ratio to use, when using the texture.</p>
<dl>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-mediatime"><code>mediaTime</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-double" id="ref-for-idl-double②">double</a></span>
<dd data-md>
<p>The media presentation timestamp (PTS) in seconds of the frame presented (e.g.
its timestamp on the <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#dom-media-currenttime" id="ref-for-dom-media-currenttime">video.currentTime</a></code> timeline).
MAY have a zero value for live-streams or WebRTC applications.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-presentedframes"><code>presentedFrames</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long⑥">unsigned long</a></span>
<dd data-md>
<p>A count of the number of frames submitted for composition. Allows clients
to determine if frames were missed between <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback④">VideoFrameRequestCallback</a></code>s. MUST be monotonically
increasing.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-processingduration"><code>processingDuration</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-double" id="ref-for-idl-double③">double</a></span>
<dd data-md>
<p>The elapsed duration in seconds from submission of the encoded packet with the same
presentation timestamp (PTS) as this frame (e.g. same as the <code class="idl"><a data-link-type="idl" href="#dom-videoframecallbackmetadata-mediatime" id="ref-for-dom-videoframecallbackmetadata-mediatime①">mediaTime</a></code>) to the decoder
until the decoded frame was ready for presentation.</p>
<dd data-md>
<p>In addition to decoding time, may include processing time. E.g., YUV
conversion and/or staging into GPU backed memory.</p>
<dd data-md>
<p>SHOULD be present. In some cases, user-agents might not be able to surface this information since
portions of the media pipeline might be owned by the OS.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-capturetime"><code>captureTime</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp⑥">DOMHighResTimeStamp</a></span>
<dd data-md>
<p>For video frames coming from a local source, this is the time at which
the frame was captured by the camera.
For video frames coming from remote source, the capture time is based on
the RTP timestamp of the frame and estimated using clock synchronization.
This is best effort and can use methods like using RTCP SR as specified
in RFC 3550 Section 6.4.1, or by other alternative means if use by
RTCP SR isn’t feasible.</p>
<dd data-md>
<p>SHOULD be present for WebRTC or getUserMedia applications, and absent otherwise.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-receivetime"><code>receiveTime</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp⑦">DOMHighResTimeStamp</a></span>
<dd data-md>
<p>For video frames coming from a remote source, this is the
time the encoded frame was received by the platform, i.e., the time at
which the last packet belonging to this frame was received over the network.</p>
<dd data-md>
<p>SHOULD be present for WebRTC applications that receive data from a remote source,
and absent otherwise.</p>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameCallbackMetadata" data-dfn-type="dict-member" data-export id="dom-videoframecallbackmetadata-rtptimestamp"><code>rtpTimestamp</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long⑦">unsigned long</a></span>
<dd data-md>
<p>The RTP timestamp associated with this video frame.</p>
<dd data-md>
<p>SHOULD be present for WebRTC applications that receive data from a remote source,
and absent otherwise.</p>
</dl>
<h2 class="heading settled" data-level="3" id="video-frame-request-callback"><span class="secno">3. </span><span class="content">VideoFrameRequestCallback</span><a class="self-link" href="#video-frame-request-callback"></a></h2>
<pre class="idl highlight def"><c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-videoframerequestcallback"><code><c- g>VideoFrameRequestCallback</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-undefined" id="ref-for-idl-undefined"><c- b>undefined</c-></a>(<a data-link-type="idl-name" href="https://w3c.github.io/hr-time/#dom-domhighrestimestamp" id="ref-for-dom-domhighrestimestamp⑧"><c- n>DOMHighResTimeStamp</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameRequestCallback" data-dfn-type="argument" data-export id="dom-videoframerequestcallback-now"><code><c- g>now</c-></code></dfn>, <a data-link-type="idl-name" href="#dictdef-videoframecallbackmetadata" id="ref-for-dictdef-videoframecallbackmetadata①"><c- n>VideoFrameCallbackMetadata</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="VideoFrameRequestCallback" data-dfn-type="argument" data-export id="dom-videoframerequestcallback-metadata"><code><c- g>metadata</c-></code></dfn>);
</pre>
<p>Each <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback⑤">VideoFrameRequestCallback</a></code> object has a <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="canceled">canceled</dfn> boolean initially set to false.</p>
<h2 class="heading settled" data-level="4" id="video-rvfc"><span class="secno">4. </span><span class="content">HTMLVideoElement.requestVideoFrameCallback()</span><a class="self-link" href="#video-rvfc"></a></h2>
<pre class="idl highlight def"><c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement①"><c- g>HTMLVideoElement</c-></a> {
<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long⑧"><c- b>unsigned</c-> <c- b>long</c-></a> <a class="idl-code" data-link-type="method" href="#dom-htmlvideoelement-requestvideoframecallback" id="ref-for-dom-htmlvideoelement-requestvideoframecallback①"><c- g>requestVideoFrameCallback</c-></a>(<a data-link-type="idl-name" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback⑥"><c- n>VideoFrameRequestCallback</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="HTMLVideoElement/requestVideoFrameCallback(callback)" data-dfn-type="argument" data-export id="dom-htmlvideoelement-requestvideoframecallback-callback-callback"><code><c- g>callback</c-></code></dfn>);
<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-undefined" id="ref-for-idl-undefined①"><c- b>undefined</c-></a> <a class="idl-code" data-link-type="method" href="#dom-htmlvideoelement-cancelvideoframecallback" id="ref-for-dom-htmlvideoelement-cancelvideoframecallback"><c- g>cancelVideoFrameCallback</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long" id="ref-for-idl-unsigned-long⑨"><c- b>unsigned</c-> <c- b>long</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="HTMLVideoElement/cancelVideoFrameCallback(handle)" data-dfn-type="argument" data-export id="dom-htmlvideoelement-cancelvideoframecallback-handle-handle"><code><c- g>handle</c-></code></dfn>);
};
</pre>
<h3 class="heading settled" data-level="4.1" id="video-rvfc-methods"><span class="secno">4.1. </span><span class="content">Methods</span><a class="self-link" href="#video-rvfc-methods"></a></h3>
<p>Each <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement②">HTMLVideoElement</a></code> has a <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="list-of-video-frame-request-callbacks">list of video frame request callbacks</dfn>, which is initially
empty. It also has a <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="last-presented-frame-identifier">last presented frame identifier</dfn> and a <dfn class="dfn-paneled" data-dfn-type="dfn" data-lt="video frame request callback identifier" data-noexport id="video-frame-request-callback-identifier">video frame request
callback identifier</dfn>, which are both numbers which are initially zero.</p>
<dl>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="HTMLVideoElement" data-dfn-type="method" data-export id="dom-htmlvideoelement-requestvideoframecallback"><code>requestVideoFrameCallback(<var>callback</var>)</code></dfn>
<dd data-md>
<p>Registers a callback to be fired the next time a frame is presented to the compositor.</p>
<p>When <code>requestVideoFrameCallback</code> is called, the user agent MUST run the following steps:</p>
<ol>
<li data-md>
<p>Let <var>video</var> be the <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement③">HTMLVideoElement</a></code> on which <code>requestVideoFrameCallback</code> is
invoked.</p>
<li data-md>
<p>Increment <var>video</var>’s <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#dom-node-ownerdocument" id="ref-for-dom-node-ownerdocument">ownerDocument</a></code>'s <a data-link-type="dfn" href="#video-frame-request-callback-identifier" id="ref-for-video-frame-request-callback-identifier">video frame request callback identifier</a> by one.</p>
<li data-md>
<p>Let <var>callbackId</var> be <var>video</var>’s <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#dom-node-ownerdocument" id="ref-for-dom-node-ownerdocument①">ownerDocument</a></code>'s <a data-link-type="dfn" href="#video-frame-request-callback-identifier" id="ref-for-video-frame-request-callback-identifier①">video frame request callback identifier</a></p>
<li data-md>
<p>Append <var>callback</var> to <var>video</var>’s <a data-link-type="dfn" href="#list-of-video-frame-request-callbacks" id="ref-for-list-of-video-frame-request-callbacks">list of video frame request callbacks</a>, associated with <var>callbackId</var>.</p>
<li data-md>
<p>Return <var>callbackId</var>.</p>
</ol>
<dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="HTMLVideoElement" data-dfn-type="method" data-export id="dom-htmlvideoelement-cancelvideoframecallback"><code>cancelVideoFrameCallback(<var>handle</var>)</code></dfn>
<dd data-md>
<p>Cancels an existing video frame request callback given its handle.</p>
<p>When <code>cancelVideoFrameCallback</code> is called, the user agent MUST run the following steps:</p>
<ol>
<li data-md>
<p>Let <var>video</var> be the target <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement④">HTMLVideoElement</a></code> object on which <code>cancelVideoFrameCallback</code> is invoked.</p>
<li data-md>
<p>Find the entry in <var>video</var>’s <a data-link-type="dfn" href="#list-of-video-frame-request-callbacks" id="ref-for-list-of-video-frame-request-callbacks①">list of video frame request callbacks</a> that is associated with the value <var>handle</var>.</p>
<li data-md>
<p>If there is such an entry, set its <a data-link-type="dfn" href="#canceled" id="ref-for-canceled">canceled</a> boolean to <code>true</code> and remove it from <var>video</var>’s <a data-link-type="dfn" href="#list-of-video-frame-request-callbacks" id="ref-for-list-of-video-frame-request-callbacks②">list of video frame request callbacks</a>.</p>
</ol>
</dl>
<h3 class="heading settled" data-level="4.2" id="video-rvfc-procedures"><span class="secno">4.2. </span><span class="content">Procedures</span><a class="self-link" href="#video-rvfc-procedures"></a></h3>
<p>An <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement⑤">HTMLVideoElement</a></code> is considered to be an <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="associated-video-element">associated video element</dfn> of a <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#document" id="ref-for-document">Document</a></code> <var>doc</var> if its <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#dom-node-ownerdocument" id="ref-for-dom-node-ownerdocument②">ownerDocument</a></code> attribute is the same as <var>doc</var>.</p>
<div class="algorithm" data-algorithm="video-rvfc-rendering-step">
<p class="issue" id="issue-9a108000"><a class="self-link" href="#issue-9a108000"></a> This spec should eventually be merged into the HTML spec, and we should directly call <a data-link-type="dfn" href="#run-the-video-frame-request-callbacks" id="ref-for-run-the-video-frame-request-callbacks">run the
video frame request callbacks</a> from the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering" id="ref-for-update-the-rendering①">update the rendering</a> steps. This procedure describes
where and how to invoke the algorithm in the meantime.</p>
<p>When the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering" id="ref-for-update-the-rendering②">update the rendering</a> algorithm is invoked, run this new step:</p>
<ul>
<li data-md>
<p>For each <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/document-sequences.html#fully-active" id="ref-for-fully-active">fully active</a> <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#document" id="ref-for-document①">Document</a></code> in <var>docs</var>, for each <a data-link-type="dfn" href="#associated-video-element" id="ref-for-associated-video-element">associated video element</a> for that <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#document" id="ref-for-document②">Document</a></code>, <a data-link-type="dfn" href="#run-the-video-frame-request-callbacks" id="ref-for-run-the-video-frame-request-callbacks①">run the video frame request callbacks</a> passing <var>now</var> as the timestamp.</p>
</ul>
<p>immediately before this existing step:</p>
<ul>
<li data-md>
<p>"<i>For each <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/document-sequences.html#fully-active" id="ref-for-fully-active①">fully active</a> <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#document" id="ref-for-document③">Document</a></code> in <var>docs</var>, <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/imagebitmap-and-animations.html#run-the-animation-frame-callbacks" id="ref-for-run-the-animation-frame-callbacks">run the animation frame callbacks</a> for that <code class="idl"><a data-link-type="idl" href="https://dom.spec.whatwg.org/#document" id="ref-for-document④">Document</a></code>, passing in <var>now</var> as the timestamp</i>"</p>
</ul>
<p>using the definitions for <var>docs</var> and <var>now</var> described in the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering" id="ref-for-update-the-rendering③">update the rendering</a> algorithm.</p>
</div>
<div class="algorithm" data-algorithm="run the video frame request callbacks">
<p class="note" role="note"><span class="marker">Note:</span> The effective rate at which <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback⑦">callbacks</a></code> are run is the lesser rate
between the video’s rate and the browser’s rate. When the video rate is lower than the browser rate,
the <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback⑧">callbacks</a></code>' rate is limited by the frequency at which new frames are
presented. When the video rate is greater than the browser rate, the <code class="idl"><a data-link-type="idl" href="#callbackdef-videoframerequestcallback" id="ref-for-callbackdef-videoframerequestcallback⑨">callbacks</a></code>' rate is limited by the frequency of the <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering" id="ref-for-update-the-rendering④">update the
rendering</a> steps. This means, a 25fps video playing in a browser that paints at 60Hz would fire
callbacks at 25Hz; a 120fps video in that same 60Hz browser would fire callbacks at 60Hz.</p>
<p>To <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="run-the-video-frame-request-callbacks">run the video frame request callbacks</dfn> for a <code class="idl"><a data-link-type="idl" href="https://html.spec.whatwg.org/multipage/media.html#htmlvideoelement" id="ref-for-htmlvideoelement⑥">HTMLVideoElement</a></code> <var>video</var> with a timestamp <var>now</var>, run the following steps:</p>
<ol>