Allow delaying autoplay until video elements become visible

Zhiqiang Zhang · foolip · commit 8ebd581ea848 · 2016-06-22T17:07:37.000+02:00
Starting autoplay when media elements loaded is too agressive. Added supplementary saying that the user agent may delay autoplay until video elements become visible. PR: #1409
diff --git a/source b/source
@@ -29967,6 +29967,10 @@ interface <dfn>HTMLVideoElement</dfn> : <span>HTMLMediaElement</span> {
   <p>The <span>default object size</span> is a width of 300 <span data-x="'px'">CSS pixels</span>
   and a height of 150 <span data-x="'px'">CSS pixels</span>. <ref spec=CSSIMAGES></p>
 
+  <p>A <code>video</code> element is said to <dfn>intersect the viewport</dfn> when it is
+  <span>being rendered</span> and its associated CSS layout box intersects the
+  <span>viewport</span>.</p>
+
   <hr>
 
   <p>User agents should provide controls to enable or disable the display of closed captions, audio
@@ -32598,12 +32602,20 @@ interface <dfn>HTMLMediaElement</dfn> : <span>HTMLElement</span> {
       data-x="dom-media-paused">paused</code> attribute is false, <span>notify about playing</span>
       for the element.</p>
 
-      <p>If the <span>autoplaying flag</span> is true, and the <code
-      data-x="dom-media-paused">paused</code> attribute is true, and the <span>media element</span>
-      has an <code data-x="attr-media-autoplay">autoplay</code> attribute specified, and the
-      <span>media element</span>'s <span>node document</span>'s <span>active sandboxing flag set</span>
-      does not have the <span>sandboxed automatic features browsing context flag</span> set, then
-      the user agent may also run the following substeps:</p>
+      <p>The user agent must <span>queue a task</span> to <span>fire a simple event</span> named
+      <code data-x="event-media-canplaythrough">canplaythrough</code> at the element.</p>
+
+      <p>If the element is not <span>eligible for autoplay</span>, then the user agent must abort
+      these substeps.</p>
+
+      <p>The user agent may run the following substeps immediately. Alternatively, if the element is
+      a <code>video</code> element, the user agent may wait until the element <span
+      data-x="intersect the viewport">intersects the viewport</span> and, if the element is still
+      <span>eligible for autoplay</span>, run the following substeps:</p>
+
+      <p class="note">This specification doesn't define the precise timing for when the intersection
+      is tested, but it is recommended that the timing match that of the Intersection Observer
+      API. <ref spec=INTERSECTIONOBSERVER></p>
 
       <ol>
 
@@ -32626,9 +32638,6 @@ interface <dfn>HTMLMediaElement</dfn> : <span>HTMLElement</span> {
       data-x="attr-media-autoplay">autoplay</code> attribute rather than using script to force the
       video to play, so as to allow the user to override the behaviour if so desired.</p>
 
-      <p>In any case, the user agent must finally <span>queue a task</span> to <span>fire a simple
-      event</span> named <code data-x="event-media-canplaythrough">canplaythrough</code> at the element.</p>
-
      </dd>
 
     </dl>
@@ -32772,6 +32781,12 @@ interface <dfn>HTMLMediaElement</dfn> : <span>HTMLElement</span> {
   data-x="dom-media-readyState">readyState</code> attribute changing to a value lower than <code
   data-x="dom-media-HAVE_FUTURE_DATA">HAVE_FUTURE_DATA</code>.</p>
 
+  <p>A <span>media element</span> is said to be <dfn>eligible for autoplay</dfn> when its
+  <span>autoplaying flag</span> is true, its <code data-x="dom-media-paused">paused</code> attribute
+  is true, the element has an <code data-x="attr-media-autoplay">autoplay</code> attribute
+  specified, and the element's <span>node document</span>'s <span>active sandboxing flag set</span>
+  does not have the <span>sandboxed automatic features browsing context flag</span> set.</p>
+
   <p>A <span>media element</span> is said to have <dfn>ended playback</dfn> when:</p>
 
   <ul>
@@ -119776,6 +119791,7 @@ INSERT INTERFACES HERE
   Yonathan Randolph,
   Yuzo Fujishima,
   Zhenbin Xu,
+  &#24352;&#26234;&#24378; (Zhiqiang Zhang),
   Zoltan Herczeg,
   and
   &Oslash;istein E. Andersen,
