mltframework / mltframework/mlt
Seeking DVB-S2 recording backwards frame-by-frame displays wrong frames
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Description
I've got various DVB-S2 recordings (H.264, 720p50) which I wanted to cut in kdenlive but there is one issue with the seeking (KDE Bug 361966). Since melt shows the same behavior, we suspect it's either a melt or ffmpeg issue.
Seeking forward frame-by-frame is fine, but seeking backward frame-by-frame often shows the same picture for several frames and then skips a few and also prints "co located POCs unavailable".
My initial guess is that the rendering is messed up for non-I(DR) frames when seeking backwards, because when I convert the recording into H.264 with keyint=1 in advance, everything works perfectly.
I'm running melt 6.4.1 on debian stretch.
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First steps
- Read the whole issue, then the project's contributing guide.
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- Open a pull request that references the issue number.
Research direction
Start by reproducing the backward frame-by-frame behavior in melt with the described DVB-S2 H.264 720p50 recordings, and compare it with forward seeking and keyint=1 conversions. Investigate whether the behavior belongs to melt or ffmpeg, using the “co located POCs unavailable” message as a clue. Done means backward stepping shows the correct frames without skips or repeated pictures.
Written by the indexing model from the issue text.
Assessment
- 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