Title: [258844] trunk/Source/WebCore
- Revision
- 258844
- Author
- [email protected]
- Date
- 2020-03-23 08:27:38 -0700 (Mon, 23 Mar 2020)
Log Message
[MSE][GStreamer] Clean and explain first sample PTS hack
https://bugs.webkit.org/show_bug.cgi?id=209335
Reviewed by Philippe Normand.
MediaSample::applyPtsOffset() had a rather confusing name, so it has
been changed to something more descriptive of its actual function:
extendToTheBeginning().
Also, its only argument has been removed, as it's always zero.
An explanation of the hack has also been added.
This patch introduces no behavior changes.
* platform/graphics/gstreamer/MediaSampleGStreamer.cpp:
(WebCore::MediaSampleGStreamer::extendToTheBeginning):
(WebCore::MediaSampleGStreamer::applyPtsOffset): Deleted.
* platform/graphics/gstreamer/MediaSampleGStreamer.h:
* platform/graphics/gstreamer/mse/AppendPipeline.cpp:
(WebCore::AppendPipeline::appsinkNewSample):
Modified Paths
Diff
Modified: trunk/Source/WebCore/ChangeLog (258843 => 258844)
--- trunk/Source/WebCore/ChangeLog 2020-03-23 15:25:39 UTC (rev 258843)
+++ trunk/Source/WebCore/ChangeLog 2020-03-23 15:27:38 UTC (rev 258844)
@@ -1,3 +1,27 @@
+2020-03-23 Alicia Boya García <[email protected]>
+
+ [MSE][GStreamer] Clean and explain first sample PTS hack
+ https://bugs.webkit.org/show_bug.cgi?id=209335
+
+ Reviewed by Philippe Normand.
+
+ MediaSample::applyPtsOffset() had a rather confusing name, so it has
+ been changed to something more descriptive of its actual function:
+ extendToTheBeginning().
+
+ Also, its only argument has been removed, as it's always zero.
+
+ An explanation of the hack has also been added.
+
+ This patch introduces no behavior changes.
+
+ * platform/graphics/gstreamer/MediaSampleGStreamer.cpp:
+ (WebCore::MediaSampleGStreamer::extendToTheBeginning):
+ (WebCore::MediaSampleGStreamer::applyPtsOffset): Deleted.
+ * platform/graphics/gstreamer/MediaSampleGStreamer.h:
+ * platform/graphics/gstreamer/mse/AppendPipeline.cpp:
+ (WebCore::AppendPipeline::appsinkNewSample):
+
2020-03-23 Zalan Bujtas <[email protected]>
[LFC] Remove unused LayoutAncestorIterator class
Modified: trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.cpp (258843 => 258844)
--- trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.cpp 2020-03-23 15:25:39 UTC (rev 258843)
+++ trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.cpp 2020-03-23 15:27:38 UTC (rev 258844)
@@ -95,12 +95,13 @@
return adoptRef(*gstreamerMediaSample);
}
-void MediaSampleGStreamer::applyPtsOffset(MediaTime timestampOffset)
+void MediaSampleGStreamer::extendToTheBeginning()
{
- if (m_pts > timestampOffset) {
- m_duration = m_duration + (m_pts - timestampOffset);
- m_pts = timestampOffset;
- }
+ // Only to be used with the first sample, as a hack for lack of support for edit lists.
+ // See AppendPipeline::appsinkNewSample()
+ ASSERT(m_dts == MediaTime::zeroTime());
+ m_duration += m_pts;
+ m_pts = MediaTime::zeroTime();
}
void MediaSampleGStreamer::offsetTimestampsBy(const MediaTime& timestampOffset)
Modified: trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.h (258843 => 258844)
--- trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.h 2020-03-23 15:25:39 UTC (rev 258843)
+++ trunk/Source/WebCore/platform/graphics/gstreamer/MediaSampleGStreamer.h 2020-03-23 15:27:38 UTC (rev 258844)
@@ -38,7 +38,7 @@
static Ref<MediaSampleGStreamer> createFakeSample(GstCaps*, MediaTime pts, MediaTime dts, MediaTime duration, const FloatSize& presentationSize, const AtomString& trackId);
- void applyPtsOffset(MediaTime);
+ void extendToTheBeginning();
MediaTime presentationTime() const override { return m_pts; }
MediaTime decodeTime() const override { return m_dts; }
MediaTime duration() const override { return m_duration; }
Modified: trunk/Source/WebCore/platform/graphics/gstreamer/mse/AppendPipeline.cpp (258843 => 258844)
--- trunk/Source/WebCore/platform/graphics/gstreamer/mse/AppendPipeline.cpp 2020-03-23 15:25:39 UTC (rev 258843)
+++ trunk/Source/WebCore/platform/graphics/gstreamer/mse/AppendPipeline.cpp 2020-03-23 15:27:38 UTC (rev 258844)
@@ -474,10 +474,23 @@
return;
}
- // Add a gap sample if a gap is detected before the first sample.
+ // Hack, rework when GStreamer >= 1.16 becomes a requirement:
+ // We're not applying edit lists. GStreamer < 1.16 doesn't emit the correct segments to do so.
+ // GStreamer fix in https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/commit/c2a0da8096009f0f99943f78dc18066965be60f9
+ // Also, in order to apply them we would need to convert the timestamps to stream time, which we're not currently
+ // doing for consistency between GStreamer versions.
+ //
+ // In consequence, the timestamps we're handling here are unedited track time. In track time, the first sample is
+ // guaranteed to have DTS == 0, but in the case of streams with B-frames, often PTS > 0. Edit lists fix this by
+ // offsetting all timestamps by that amount in movie time, but we can't do that if we don't have access to them.
+ // (We could assume the track PTS of the sample with track DTS = 0 is the offset, but we don't have any guarantee
+ // we will get appended that sample first, or ever).
+ //
+ // Because a track presentation time starting at some close to zero, but not exactly zero time can cause unexpected
+ // results for applications, we extend the duration of this first sample to the left so that it starts at zero.
if (mediaSample->decodeTime() == MediaTime::zeroTime() && mediaSample->presentationTime() > MediaTime::zeroTime() && mediaSample->presentationTime() <= MediaTime(1, 10)) {
- GST_DEBUG("Adding gap offset");
- mediaSample->applyPtsOffset(MediaTime::zeroTime());
+ GST_DEBUG("Extending first sample to make it start at PTS=0");
+ mediaSample->extendToTheBeginning();
}
m_sourceBufferPrivate->didReceiveSample(mediaSample.get());
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