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  • FFMPEG Seeking with concat demuxer causes video & audio to be out of sync

    20 février 2023, par Garuuk

    I have a very simple use case that's driving me bananas.

    


    My problem and question :

    


    I'm using ffmpeg version 5.1.2 on a MacOS and i'm using ffmpeg seeking and concat demuxer to cut many 1 minute videos into 15 seconds chopped up over 12 clips where every clip is just 2 seconds from the same video (kind of like a mini teasers for the video). I would really like to not have to re-encode to make the video processing as fast as possible.

    


    First, I take each 1 minute video and cut it up into 12 clips (I do all this programmatically in python fwiw)

    


    ffmpeg -ss 0 -i input.mp4 -t 2 -c copy -y cut_1.mp4
ffmpeg -ss 4 -i input.mp4 -t 2 -c copy -y cut_2.mp4
ffmpeg -ss 8 -i input.mp4 -t 2 -c copy -y cut_3.mp4
...
...


    


    I then write all the output file names to my concat_manifest.txt

    


    file cut_1.mp4
file cut_2.mp4
...
...


    


    Then I run my concat command :

    


    ffmpeg -f concat -i concat_manifest.txt -c copy -y concat_video.mp4


    


    This works really fast but the audio and video at the stitch point get out of sync and sometimes the video just chokes & lags. It's mostly not a smooth experience.

    


    What I have tried :

    


      

    1. using the concat protocol with intermediate profiles : ffmpeg.org/wiki/Concatenate#demuxer

      2. 


    2. Putting the -ss when I seek after the -i. This makes everything worse

      3. 


    3. Playing around with different -ss values. This has some noticeable affects but it's not obvious why yet.

      4. 


    4. I've also read from the ffmpeg resource regarding seeking and copying :

      5. 


    


    Which leads me to believe that maybe because ffmpeg is using timestamps instead of frames, seeking isn't accurate using -ss when using the concat demuxer

    


    Is there a way to get concat demuxer cutting and concatenating the video where the audio is somewhat in sync with the video ?

    


    Thanks

    


    EDIT : I found an answer and i'll be posting the solution in the coming few days.

    


  • Revision 100192 : $val[’htpass’] est défini plus haut, qui plus est là on le rendait vide

    26 octobre 2016, par kent1@… — Log

    $valhtpass ? est défini plus haut, qui plus est là on le rendait vide

  • Revision 100192 : $val[’htpass’] est défini plus haut, qui plus est là on le rendait vide

    26 octobre 2016, par kent1@… — Log

    $valhtpass ? est défini plus haut, qui plus est là on le rendait vide

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