Hi Josh, On Tue, 22 Dec 2020, Josh Allmann wrote:
Thank you for taking the time to look into this! Tested with your alternative patch and it does seem to be an improvement. I was able to find a case where it didn't seem to do the correct thing (described below), but this is not a regression; master doesn't do the correct thing, and neither does my patch. I haven't looked much at what the code is doing beyond running these tests, but could find some time to dig in early 2021 if it's not fixed by then. First, a working sample with pts > 0 . This has a 600-frame GOP (20s @ 30fps) to show that cutting mid-GOP works correctly. https://trac.ffmpeg.org/raw-attachment/ticket/9028/gop-600.mp4 Command to generate a clipped sample with edit list. This spans two GOPs. ffmpeg -ss 17.316666999999999 -i gop-600.mp4 -t 5 -c copy -movflags +faststart -y cut-mp4-600.mp4 Things look good with ffprobe, and playback works well with ffplay; it starts right around the 17-second mark. The sample is a timecode pattern so it is easy to verify. If the sample is a mpegts (rather than a mp4, all other things identical), then things are a bit odd: https://trac.ffmpeg.org/raw-attachment/ticket/9028/gop-600.ts Cut the sample with: ffmpeg -ss 17.316666999999999 -i gop-600.ts -t 5 -c copy -movflags +faststart -y cut-ts-600.mp4 Probing gives the correct duration with a start time of 2.683. However, playback starts at the 20 second mark. (Same timecode pattern, so easy to visually verify.) Incidentally, it seems that 20 - 2.683 = 17.316, which is the original cut position. ffprobe cut-ts-600.mp4 gives "Duration: 00:00:05.12, start: 2.683000" The trac ticket has a bit more info (including commands for how to generate the samples) but this is the gist of it.
I think this issue isn't related to the mov muxer at least, but is more related to how stream copy works at the ffmpeg.c level, and/or how the seeking is done.
As that's unrelated, and I haven't heard any objections to my version of the patch, I think I'll go ahead and land it soon then.
// Martin _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
