livepeer / livepeer/lpms

Number of encoded frames does not match number of decoded frames

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Dominant language
Go
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283
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72
Avg merge
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Merged PRs (30d)
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Description

Under particular conditions, the number of encoded frames does not match number of decoded frames.

* Reproducible case that encodes 61 "frames" (61 frames encoded and 61 packets muxed) but only decodes 60, as shown below.
* FFProbe mirrors our numbers: it reads the same 61 packets in the bitstream, but only decodes 60 frames.
* This only seems to happen with the MP4 muxer. The mpegts muxer works as expected.
* Possible that this is a separate slice / field / etc but this doesn't seem likely.
* If this is indeed a non-display frame of some sort : is there a way to detect this?
https://github.com/livepeer/lpms/blob/d722afc1dfa0e7b7102db8b67588a00be6dfd938/ffmpeg/ffmpeg_test.go#L1117-L1209

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Research direction

Start with the reproducible case in ffmpeg/ffmpeg_test.go around lines 1117-1209 and compare the MP4 and mpegts muxer results. Verify the 61 encoded and muxed packets versus 60 decoded frames, compare with FFProbe, and determine whether the extra packet is a non-display frame and how it can be detected.

Written by the indexing model from the issue text.

Assessment

Tech stack
go
Domain
audio-video-rtc
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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