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• Creating audio segments of identical duration using FFmpeg

  22 mars 2023, par aradalvand

  I have an MP4 file with one video stream and one audio stream. I want to divide each stream into 2-second segments. For the video, I know that I need to have a keyframe (I-frame) precisely every 2 seconds in order for it be to able to be divided into exactly 2-second segments ; which can be achieved via FFmpeg's force_key_frames option, set to a value like expr:gte(t,n_forced*2).

  


  For the audio stream, however, I can't seem to get the segments to be identical in duration. The force_key_frames option is only applicable to videos, and I'm not sure what the equivalent of that would be for audio streams.

  


  This is the FFmpeg command I'm using :

  


  ffmpeg -i input.mp4 \
    -map 0:a \
    -f segment \
    -segment_time 2 \
    -segment_list output/playlist.m3u8 \
    -segment_format mpegts \
    output/seg-%d.ts


  


  And this is the resulting playlist.m3u8 file :

  


  #EXTM3U
#EXT-X-VERSION:3
#EXT-X-MEDIA-SEQUENCE:0
#EXT-X-ALLOW-CACHE:YES
#EXT-X-TARGETDURATION:3
#EXTINF:2.011433,
seg-0.ts
#EXTINF:2.011422,
seg-1.ts
#EXTINF:1.985300,
seg-2.ts
#EXTINF:2.011433,
seg-3.ts
#EXTINF:1.985300,
seg-4.ts
#EXTINF:2.011433,
seg-5.ts
#EXTINF:1.985300,
seg-6.ts
#EXTINF:2.011433,
seg-7.ts
#EXTINF:2.011422,
seg-8.ts
#EXTINF:1.985311,
seg-9.ts
#EXTINF:2.011433,
seg-10.ts
#EXTINF:1.985300,
seg-11.ts
#EXTINF:2.011433,
seg-12.ts
#EXTINF:1.985300,
seg-13.ts
#EXTINF:2.011433,
seg-14.ts
#EXTINF:1.985300,
seg-15.ts
#EXTINF:2.011433,
seg-16.ts
#EXTINF:2.011422,
seg-17.ts
#EXTINF:1.985300,
seg-18.ts
#EXTINF:2.011433,
seg-19.ts
#EXTINF:1.985300,
seg-20.ts
#EXTINF:2.011433,
seg-21.ts
#EXTINF:1.985300,
seg-22.ts
#EXTINF:2.011433,
seg-23.ts
#EXTINF:2.011422,
seg-24.ts
#EXTINF:1.985311,
seg-25.ts
#EXTINF:2.011433,
seg-26.ts
#EXTINF:1.985300,
seg-27.ts
#EXTINF:2.011433,
seg-28.ts
#EXTINF:1.985300,
seg-29.ts
#EXTINF:0.052244,
seg-30.ts
#EXT-X-ENDLIST


  


  As you can see, the segments aren't precisely 2 seconds.
I don't know much about how audio works under the hood, so I don't understand why FFmpeg doesn't seem to be able to divide the audio into segments that all have precisely the duration I specify.

  


  I would also like to know whether anything can be done (analogous to force_key_frames for videos) to solve this problem.

  


  Thank you.

  


• fftools/ffmpeg : reduce -re to -readrate 1

  2 mai 2023, par Anton Khirnov

  fftools/ffmpeg : reduce -re to -readrate 1
  They are exactly equivalent, so there is no point in maintaining a
  
  separate flag for -re.
  

  • [DH] fftools/ffmpeg.c
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_demux.c

• lavfi/vf_libplacebo : switch to activate()

  6 mai 2023, par Niklas Haas

  lavfi/vf_libplacebo : switch to activate()
  To present compatibility with the current behavior, we keep track of a
  
  FIFO of exact frame timestamps that we want to output to the user. In
  
  practice, this is essentially equivalent to the current filter_frame()
  
  code, but this design allows us to scale to more complicated use cases
  
  in the future - for example, insertion of intermediate frames
  
  (deinterlacing, frame doubling, conversion to fixed fps, ...)
  

  • [DH] libavfilter/vf_libplacebo.c