Try set-pts=0 as a filter On Fri, Jan 24, 2020 at 5:24 PM George R. Welch <geo...@grwelch.com> wrote:
> Greetings, > > I get video files from another division. It is my task to cut out a > part of the video, and replace it with a part I create. The videos I > receive are h264 with aac audio. It is very strongly hoped that this > can be done without re-encoding the parts of the original which we keep. > > I have been using ffmpeg for cutting up the file I receive, and I've > been using the concat demuxer to concatenate the pieces of the original > with the part I make. This has worked well (over a dozen times) until > recently. > > In order for concat to work correctly, I take care to make sure the > video I make fits the one I am inserting it into (same frame rate, refs, > etc). I also take care to only cut the original movie at I frames. > > I have run into trouble with the most recent job. When I concatenate > the parts, there is a slight glitch when it transitions from the part I > made to the other. > > As far as I can tell, the only thing that is different from the previous > runs is that the file I am given is encoded with B frames, whereas that > had never happened before. > > An oddity is that when I cut the original video, the timestamp does not > begin at zero: > > $ ffmpeg -i input.mkv -ss [start-time] -t [duration] -c copy part1.mkv > [seems to work] > > Now look at the result: > > $ ffprobe -hide_banner -show_frames -select_streams v part1.mkv > > Here is the first frame: > > [FRAME] > media_type=video > stream_index=0 > key_frame=1 > pkt_pts=1968 > pkt_pts_time=1.968000 > pkt_dts=1968 > pkt_dts_time=1.968000 > best_effort_timestamp=1968 > best_effort_timestamp_time=1.968000 > ... > > I don't understand why the first frame does not start at zero. I have > tried adding "-seek_timestamp 1" but it has no effect. > > When I use concat to place this part after my video, then there is a > glitch at the transition. > > However, if I change the flag to the input: > > $ ffmpeg -ss [start-time] -i input.mkv -t [duration] -c copy part1.mkv > > then ffmpeg generates some errors: > > [matroska @ 0x7ffadb028600] failed to avoid negative pts -58 in stream 1. > Try -avoid_negative_ts 1 as a possible workaround. > > Repeating the command with -avoid -avoid_negative_ts 1 still generates > the same message, and the output is the same. > > Now when I look at the first frame it does start at zero, but there is > still a glitch at the transition after concatenating. > > Does anyone have any suggestions? Is it impossible to concat segments > with B frames? > > Thank you in advance, > > --George > > _______________________________________________ > ffmpeg-user mailing list > ffmpeg-user@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe". _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
