Open
Bug 1470249
Opened 6 years ago
Updated 2 years ago
Webrtc Video clock and Audio clock appear to advance at different wall-clock speeds but the RTCP offset remains constant.
Categories
(Core :: WebRTC: Audio/Video, defect, P3)
Core
WebRTC: Audio/Video
Tracking
()
NEW
People
(Reporter: bowljoman, Unassigned)
References
Details
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.87 Safari/537.36
Steps to reproduce:
I initiated a session with firefox publishing h264 and opus.
I traced out the rtp timestamps received on both channels and un-scaled them at 48k audio and 90k video.
I also counted bytes decoded from audio and counted them(monitoring dropped packets, etc).
Actual results:
I found that audio packet times and audio bytes decoded both resolved to exact parity . Video packet times advance at a faster wall clock rate, such that muxing the audio and video into a media file results in growing synchronization issues.
I then looked at RTCP for the offset and expected the offset to change with the advancing video drift. It did not.
Expected results:
un-scaled video and audio times should advance at the same wall clock rate.
I expect un-scaled video and audio stream times to be within 500 milliseconds of each other at the receiver with RTCP providing the _exact_ offset, and updating the offset when drift is unavoidable and detected.
perfect conditions would be drift free, using a shared clock(audio's), and perfectly muxed out-bound regarding incremented stream time.
* unscaled time is transforming RTP packet times to linear stream time
Updated•6 years ago
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Component: Untriaged → WebRTC: Audio/Video
Product: Firefox → Core
Comment 1•6 years ago
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I'd believe this. We don't have any special logic re-clocking video to the audio domain. We just clock video as it comes in on both the sending and receiving side.
We do have plans to re-clock it properly. I'll put this into the dependency tree so we can keep track.
Updated•2 years ago
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Severity: normal → S3
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Description
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