[webkit-changes] [WebKit/WebKit] ced7f5: [MediaRecorder] timecode provided in BlobEvent is ...

[Jean-Yves Avenard]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: ced7f5e2066e77bb308efb5274a69119421cfd81
      https://github.com/WebKit/WebKit/commit/ced7f5e2066e77bb308efb5274a69119421cfd81
  Author: Jean-Yves Avenard <jya at apple.com>
  Date:   2024-11-11 (Mon, 11 Nov 2024)

  Changed paths:
    A LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/MediaRecorder-blob-timecode.https-expected.txt
    A LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/MediaRecorder-blob-timecode.https.html
    M LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/w3c-import.log
    M LayoutTests/platform/glib/TestExpectations
    M Source/WebCore/Modules/mediarecorder/MediaRecorder.cpp
    M Source/WebCore/Modules/mediarecorder/MediaRecorder.h
    M Source/WebCore/platform/mediarecorder/MediaRecorderPrivateEncoder.cpp
    M Source/WebCore/platform/mediarecorder/MediaRecorderPrivateEncoder.h

  Log Message:
  -----------
  [MediaRecorder] timecode provided in BlobEvent is incorrect
https://bugs.webkit.org/show_bug.cgi?id=282320
rdar://138895100

Reviewed by Anne van Kesteren.

The timecode returned was always of the time at which requestData() was called and not
"For a MediaRecorder instance, the timecode in the first produced BlobEvent MUST contain 0.
Subsequent BlobEvent's timecode contain the difference of the timestamp of creation of the
first chunk in said BlobEvent and the timestamp of the first chunk of the first produced BlobEvent"

imported wpt's MediaRecorder-blob-timecode.https.html to test this functionality.
The test exposed an issue in our implementation (which the test didn't deal with).
It sets a timeslice of 0 and assume that we would always get a monotonically increasing
timecode, but if we attempts to make 0ms long segment that may not always be the case.

As a workaround, and considering real-life usage, if a timeslice is set and no data was recorded at the time
the timer occurs, we will not emit `dataavailable` event. We also limit how small the timeslice can be to 100ms.

On platforms using AVFoundation, we make the minimum segment size to be 1s. Using a MP4 recorder calling requestData()
will return empty Blobs if called before 1s of data has been accumulated due to the structure of ISOBMFF (it needs to
write a complete samples table first). An AVFormatWriter will also errors with "NotReady" if we attempt to generate
too short segments.
With WebM data is written as received, but a new cluster will always be at least one second long.

We also hold off writing any samples until the AudioSampleBufferCompressor has started to return audible data to
ensure video and audio frames are already interleaved in monotonically increasing time order.

* LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/MediaRecorder-blob-timecode.https-expected.txt: Added.
* LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/MediaRecorder-blob-timecode.https.html: Added.
* LayoutTests/imported/w3c/web-platform-tests/mediacapture-record/w3c-import.log:
* LayoutTests/platform/glib/TestExpectations:
* Source/WebCore/Modules/mediarecorder/MediaRecorder.cpp:
(WebCore::MediaRecorder::MediaRecorder):
(WebCore::MediaRecorder::startRecording):
(WebCore::MediaRecorder::requestData):
(WebCore::MediaRecorder::requestDataInternal): Split method. Don't emit dataavailable event unless we actually have new data.
* Source/WebCore/Modules/mediarecorder/MediaRecorder.h: Set a minimum timeslice of 0.1s.
* Source/WebCore/platform/mediarecorder/MediaRecorderPrivateEncoder.cpp:
(WebCore::MediaRecorderPrivateEncoder::takeData):
(WebCore::MediaRecorderPrivateEncoder::enqueueCompressedAudioSampleBuffers):
(WebCore::MediaRecorderPrivateEncoder::flushToEndSegment): Return pair returnCode/time instead of setting a member variable.
Test exposed a case where we could have not written all available frames.
(WebCore::MediaRecorderPrivateEncoder::muxNextFrame):
(WebCore::MediaRecorderPrivateEncoder::fetchData):
(WebCore::MediaRecorderPrivateEncoder::flushPendingData):
* Source/WebCore/platform/mediarecorder/MediaRecorderPrivateEncoder.h:

Canonical link: https://commits.webkit.org/286442@main



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