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• Ffmpeg : Concat multiple videos and an audio file. Videos may or may not have audio and I cant know it before runnign the command

  28 juillet 2023, par AtActionPark

  I have a list of mp4 and an aac audio file. I have a concat.txt file with all the mp4s that need to be concatenated.
I need to concat all the mp4s and merge the aac on top.

  


  As said in the title, the mp4s individually may or may not have an audio track, and I can not check the mp4s with no audio, add a dummy sound track as it will be an automated process with thousands of commands executed daily.

  


  The sound of the mp4, if present, must be preserved and merged with the aac

  


  Here is a working command for the case where at least the first of my mp4s has an audiotrack :

  


  ffmpeg -f concat -safe 0 -i concat.txt -i audio.aac  -c:v copy -filter_complex "[0:a][1:a] amix=inputs=2:duration=shortest [audio_out]" -map 0:v -map "[audio_out]" -y result.mp4


  


  However that breaks if my mp4s dont have audio

  


  


  Stream specifier ':a' in filtergraph description [0:a][1:a]
amix=inputs=2:duration=shortest [audio_out] matches no streams.

  


  


  I've been reading about anullsrc, and would like to take [0:a] if it exists, or a generated empty audio channel, and merge it with my aac, but I'm not getting there.

  


  Any help would be appreciated

  


  Thanks

  


• Concatenate sped up videos and normal speed ones using ffmpeg

  5 juillet 2020, par FlucTuAte.

  I have a python script that uses ffmpeg to cut different sections of a video. There are ones that i want to keep as-is, and i use this ffmpeg command for that :

  


  os.system((
      "ffmpeg "
      "-loglevel error "
      "-nostats "
      "-hide_banner "
      f"-ss {start / fps} "
      f"-i \"{uncutVideo}\" "
      f"-t {(end - start) / fps} "
      "-c copy "
      "-avoid_negative_ts make_zero "
      f"tmp\\out{processedClips}.mp4"
))


  


  Start and end are frame numbers, that's why i divide by fps.
Then I have the parts where I want to speed up the video. I use this command for that :

  


  os.system((
    "ffmpeg "
    "-loglevel error "
    "-nostats "
    "-hide_banner "
    f"-ss {start / fps} "
    f"-i \"{uncutVideo}\" "
    f"-t {(end - start) / fps / cfg.speed} "
    f"-vf \"setpts=PTS/{cfg.speed}\" "
    "-avoid_negative_ts make_zero "
    "-an "
    f"tmp\\out{processedClips}.mp4"
))


  


  After these are done I want to concatenate them using the concat demuxer :

  


  os.system((
    "ffmpeg "
    "-loglevel error "
    "-nostats "
    "-f concat "
    "-safe 0 "
    "-i videoClips.txt "
    "-c copy "
    f"\"{cfg.saveDir}\\{srcFileName}-Cut.mp4\""
))


  


  This runs fine, but in the output file there is a long pause when the sped up part would start. The last frame of the normal speed part is shown but the timeline shows that the video is playing. After the sped up part would have ended it shows the next normal speed part properly. This is what I see in VLC at least. I've also tried MPC-BE and MPC-HC. They also mess up but instead the sped up part is displayed properly and they pause right after. These pauses seem to be as long as the sped up part would be.

  


  What could cause this ?

  


  Any help is appreciated.

  


• Revision b0520b61ed : new unit test for cpu-speed Tests q0 ( lossless), very high bitrate and low bi

  2 juillet 2013, par Jim Bankoski

  Changed Paths :
   Modify /test/codec_factory.h

  
   Add /test/cpu_speed_test.cc

  
   Modify /test/test.mk

  
  
  new unit test for cpu-speed

  Tests q0 ( lossless), very high bitrate and low bitrates at cpu speed
  0, 1 and 2.

  Change-Id : I0c5cdca00acd8d01e7b13f124b3b08d4b1ae9f6d