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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/172506">172506</a></dd>
<dt>Author</dt> <dd>jer.noble@apple.com</dd>
<dt>Date</dt> <dd>2014-08-12 16:37:34 -0700 (Tue, 12 Aug 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>[MSE] YouTube will lose audio, video after seeking backwards to an unbuffered range.
https://bugs.webkit.org/show_bug.cgi?id=135855
Reviewed by Eric Carlson.
When seeking into an unbuffered or partially buffered range, we will unconditionally pass samples to the
decode queue even if there exist large gaps between those samples. Subsequently, the decoder will not
notify us that it has become ready for new samples until playback reaches those later samples and the samples
are discarded.
When sending samples to be decoded in provideMediaData(), stop if there exists a large gap in the sample timeline.
Do this by tracking the last enqueued decode end time, and look to see if the next sample's decode time indicates
a gap of greater than 1 second.
* Modules/mediasource/SourceBuffer.cpp:
(WebCore::SourceBuffer::TrackBuffer::TrackBuffer): Initialize lastEnqueuedDecodeEndTime.
(WebCore::SourceBuffer::seekToTime): Set needsReenqueueing, in case samples do not yet exist in the trackBuffer
sufficient to re-enqueue for the destination time, so that re-enqueueing will occur after the next append.
(WebCore::SourceBuffer::sourceBufferPrivateDidReceiveSample): Check against lastEnqueuedDecodeEndTime, rather than
lastEnqueuedPresentationTime before adding samples to the decodeQueue.
(WebCore::SourceBuffer::provideMediaData): Stop when we reach a large gap between samples.
(WebCore::SourceBuffer::reenqueueMediaForTime): Set or clear lastEnqueuedDecodeEndTime based on whether we
have appended any non-displaying samples after flushing.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreModulesmediasourceSourceBuffercpp">trunk/Source/WebCore/Modules/mediasource/SourceBuffer.cpp</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (172505 => 172506)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2014-08-12 23:15:00 UTC (rev 172505)
+++ trunk/Source/WebCore/ChangeLog 2014-08-12 23:37:34 UTC (rev 172506)
</span><span class="lines">@@ -1,3 +1,29 @@
</span><ins>+2014-08-12 Jer Noble <jer.noble@apple.com>
+
+ [MSE] YouTube will lose audio, video after seeking backwards to an unbuffered range.
+ https://bugs.webkit.org/show_bug.cgi?id=135855
+
+ Reviewed by Eric Carlson.
+
+ When seeking into an unbuffered or partially buffered range, we will unconditionally pass samples to the
+ decode queue even if there exist large gaps between those samples. Subsequently, the decoder will not
+ notify us that it has become ready for new samples until playback reaches those later samples and the samples
+ are discarded.
+
+ When sending samples to be decoded in provideMediaData(), stop if there exists a large gap in the sample timeline.
+ Do this by tracking the last enqueued decode end time, and look to see if the next sample's decode time indicates
+ a gap of greater than 1 second.
+
+ * Modules/mediasource/SourceBuffer.cpp:
+ (WebCore::SourceBuffer::TrackBuffer::TrackBuffer): Initialize lastEnqueuedDecodeEndTime.
+ (WebCore::SourceBuffer::seekToTime): Set needsReenqueueing, in case samples do not yet exist in the trackBuffer
+ sufficient to re-enqueue for the destination time, so that re-enqueueing will occur after the next append.
+ (WebCore::SourceBuffer::sourceBufferPrivateDidReceiveSample): Check against lastEnqueuedDecodeEndTime, rather than
+ lastEnqueuedPresentationTime before adding samples to the decodeQueue.
+ (WebCore::SourceBuffer::provideMediaData): Stop when we reach a large gap between samples.
+ (WebCore::SourceBuffer::reenqueueMediaForTime): Set or clear lastEnqueuedDecodeEndTime based on whether we
+ have appended any non-displaying samples after flushing.
+
</ins><span class="cx"> 2014-08-12 Commit Queue <commit-queue@webkit.org>
</span><span class="cx">
</span><span class="cx"> Unreviewed, rolling out r172494.
</span></span></pre></div>
<a id="trunkSourceWebCoreModulesmediasourceSourceBuffercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/Modules/mediasource/SourceBuffer.cpp (172505 => 172506)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/Modules/mediasource/SourceBuffer.cpp 2014-08-12 23:15:00 UTC (rev 172505)
+++ trunk/Source/WebCore/Modules/mediasource/SourceBuffer.cpp 2014-08-12 23:37:34 UTC (rev 172506)
</span><span class="lines">@@ -71,6 +71,7 @@
</span><span class="cx"> MediaTime lastFrameDuration;
</span><span class="cx"> MediaTime highestPresentationTimestamp;
</span><span class="cx"> MediaTime lastEnqueuedPresentationTime;
</span><ins>+ MediaTime lastEnqueuedDecodeEndTime;
</ins><span class="cx"> bool needRandomAccessFlag;
</span><span class="cx"> bool enabled;
</span><span class="cx"> bool needsReenqueueing;
</span><span class="lines">@@ -83,6 +84,7 @@
</span><span class="cx"> , lastFrameDuration(MediaTime::invalidTime())
</span><span class="cx"> , highestPresentationTimestamp(MediaTime::invalidTime())
</span><span class="cx"> , lastEnqueuedPresentationTime(MediaTime::invalidTime())
</span><ins>+ , lastEnqueuedDecodeEndTime(MediaTime::invalidTime())
</ins><span class="cx"> , needRandomAccessFlag(true)
</span><span class="cx"> , enabled(false)
</span><span class="cx"> , needsReenqueueing(false)
</span><span class="lines">@@ -317,6 +319,7 @@
</span><span class="cx"> TrackBuffer& trackBuffer = trackBufferPair.value;
</span><span class="cx"> const AtomicString& trackID = trackBufferPair.key;
</span><span class="cx">
</span><ins>+ trackBuffer.needsReenqueueing = true;
</ins><span class="cx"> reenqueueMediaForTime(trackBuffer, trackID, time);
</span><span class="cx"> }
</span><span class="cx"> }
</span><span class="lines">@@ -1208,7 +1211,7 @@
</span><span class="cx"> // Add the coded frame with the presentation timestamp, decode timestamp, and frame duration to the track buffer.
</span><span class="cx"> trackBuffer.samples.addSample(sample);
</span><span class="cx">
</span><del>- if (trackBuffer.lastEnqueuedPresentationTime.isInvalid() || presentationTimestamp > trackBuffer.lastEnqueuedPresentationTime) {
</del><ins>+ if (trackBuffer.lastEnqueuedDecodeEndTime.isInvalid() || decodeTimestamp >= trackBuffer.lastEnqueuedDecodeEndTime) {
</ins><span class="cx"> DecodeOrderSampleMap::KeyType decodeKey(decodeTimestamp, presentationTimestamp);
</span><span class="cx"> trackBuffer.decodeQueue.insert(DecodeOrderSampleMap::MapType::value_type(decodeKey, sample));
</span><span class="cx"> }
</span><span class="lines">@@ -1383,7 +1386,19 @@
</span><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> RefPtr<MediaSample> sample = sampleIt->second;
</span><ins>+ // Do not enqueue samples spanning a significant unbuffered gap.
+ // NOTE: one second is somewhat arbitrary. MediaSource::monitorSourceBuffers() is run
+ // on the playbackTimer, which is effectively every 350ms. Allowing > 350ms gap between
+ // enqueued samples allows for situations where we overrun the end of a buffered range
+ // but don't notice for 350s of playback time, and the client can enqueue data for the
+ // new current time without triggering this early return.
+ // FIXME(135867): Make this gap detection logic less arbitrary.
+ MediaTime oneSecond(1, 1);
+ if (trackBuffer.lastEnqueuedDecodeEndTime.isValid() && sample->decodeTime() - trackBuffer.lastEnqueuedDecodeEndTime > oneSecond)
+ break;
+
</ins><span class="cx"> trackBuffer.lastEnqueuedPresentationTime = sample->presentationTime();
</span><ins>+ trackBuffer.lastEnqueuedDecodeEndTime = sample->decodeTime() + sample->duration();
</ins><span class="cx"> m_private->enqueueSample(sample.release(), trackID);
</span><span class="cx"> #if !LOG_DISABLED
</span><span class="cx"> ++enqueuedSamples;
</span><span class="lines">@@ -1425,8 +1440,13 @@
</span><span class="cx">
</span><span class="cx"> m_private->flushAndEnqueueNonDisplayingSamples(nonDisplayingSamples, trackID);
</span><span class="cx">
</span><del>- if (!nonDisplayingSamples.isEmpty())
</del><ins>+ if (!nonDisplayingSamples.isEmpty()) {
</ins><span class="cx"> trackBuffer.lastEnqueuedPresentationTime = nonDisplayingSamples.last()->presentationTime();
</span><ins>+ trackBuffer.lastEnqueuedDecodeEndTime = nonDisplayingSamples.last()->decodeTime();
+ } else {
+ trackBuffer.lastEnqueuedPresentationTime = MediaTime::invalidTime();
+ trackBuffer.lastEnqueuedDecodeEndTime = MediaTime::invalidTime();
+ }
</ins><span class="cx">
</span><span class="cx"> // Fill the decode queue with the remaining samples.
</span><span class="cx"> trackBuffer.decodeQueue.clear();
</span></span></pre>
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