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I am encoding a video with ffmpeg into H.264 stored in an FLV container. I would like to be able to trim segments of this video out as it is still encoding. The video contains no audio.

I am encoding the video like so:

ffmpeg -i recording.mp4 -c libx264 output.flv

And I'm attempting to trim the video with:

ffmpeg -i output.flv -ss 00:00:00.000 -t 00:00:01.000 -c copy output2.mp4

While the video is still encoding, I see this error when I try to trim:

Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

Also while encoding, using ffprobe, I get information like the following:

Duration: 00:00:26.96, start: 0.080000, bitrate: 126 kb/s
  Stream #0:0: Video: h264 (High), yuv420p, 640x480, 25 fps, 25 tbr, 1k tbn, 50 tbc

How can I go about trimming this file while it's still encoding? I am willing to change container formats from flv to something else if needed. Ultimately, I need to be in mp4, but I don't mind doing some container shuffling to allow me to trim out portions while still encoding.

  • Works here. Which ffmpeg version? – Gyan May 22 '18 at 19:59
  • 2.8.14. From the official Ubuntu 16.04 repos – seanr8 May 22 '18 at 20:02
  • Get a binary from johnvansickle.com/ffmpeg and check. – Gyan May 22 '18 at 20:04
  • I just did. However, now it trims without error, but the resulting file has a length of 0 and 0 frames are in it. I used the exact same command as above, but used the build you linked to. I tried both the release and the git builds. Are you using a publicly available sample video I could find somewhere and try myself? – seanr8 May 22 '18 at 20:13
  • Do you get the same behaviour if you cut a longer segment? – PTS May 22 '18 at 21:22
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Keep FLV but trim using demuxer seek and duration.

ffmpeg -ss 00:00:03.000 -t 00:00:01.000 -i output.flv -c copy output2.mp4

Also, skip -ss if it's 0 i.e. stream start.

| improve this answer | |
  • Skipping -ss for the start is what fixed it for me. It seems like the file was really starting at 0.080. How would I know that if I were writing a script to trim a file? – seanr8 May 23 '18 at 12:29

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