I have a Zoom video that I "cut" into two videos:

ffmpeg -i 0131.mp4 -ss 55 -t 38:52 -codec copy 0131-1.mp4
ffmpeg -i 0131.mp4 -ss 40:00 -t 1:52 -codec copy 0131-2.mp4

I then merged into one using [concat demuxer][1] in ffmpeg.

The merged video plays, but the first 15 seconds of the merged video is blank (audio plays okay). What do I need to do so that first 15 seconds of the merged video also displays? Is this due to a "keyframe" not appearing for 15 seconds after my cut point?

Stream #0:0(und): Audio: aac (LC) (mp4a / 0x6134706D), 32000 Hz, mono, fltp, 126 kb/s (default)
  creation_time   : 2021-01-31T21:53:20.000000Z
  handler_name    : AAC audio
Stream #0:1(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 741 kb/s, 25 fps, 25 tbr, 30k tbn, 60k tbc (default)
  creation_time   : 2021-01-31T21:53:20.000000Z
  handler_name    : H.264/AVC video
  encoder         : AVC Coding
Stream #0:2(und): Data: bin_data (text / 0x74786574), 0 kb/s
  creation_time   : 2021-01-31T21:53:20.000000Z
  handler_name    : Text

1 Answer 1


Every time I concat, I quickly run it thru this awesome little freeware from Mean beforehand, avidemux, (MP4 Muxer->Move index to the beginning of the file->Save) and it fixes the majority of any concat issues I've run into. Not sure if it will fix your issue, but it can't hurt and somewhere down the line avidemux will come in handy and fix a concat issue if you're having one. Shoutout to Mean for such a helpful piece of freeware!

  • wonder if this is the same in ffmpeg: ffmpeg -i input.mp4 -codec copy -movflags +faststart output.mp4 (stackoverflow.com/questions/7614635/…) I tried this in ffmpeg and no difference in results. I'll try avidemux and see if its any different.
    – Sun
    Commented Feb 6, 2021 at 4:34

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