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• How to get decoded audio samples in libav

  22 mai 2020, par Desp4

  I'm trying to decode a non-planar wav audio file with libav, but the output file seems corrupted and a bit longer than the original. Am I handling frames wrong when writing them to a file like this ?

  



  


  fwrite(frame->extended_data[0], 1, frame->linesize[0], outFile);

  


  



  When opening the file in audacity it looks like this. Where two channels on top are from the original and the ones underneath are from a decoded file.

  


• wrong duration when copying audio from ts to mp2 audio

  20 décembre 2017, par Ahmed Fares

  When I copy audio from a .ts video file using ffmpeg with following command, the resulting audio file is shorter than the original file, because of the silent parts of the original file.

  ffmpeg -i InputFile.ts -vn -acodec copy OutputFile

• avconv audio and video out of sync

  28 juillet 2015, par bram_aerts

  I have a problem synchronizing audio and video using avconv.
  My goal is to process the video stream with opencv and later put the original audio back on the soundless video.
  The processed video stream will be at the same period of time as the original video, but will have a starting offset of a few minutes.

  I tried to simplify the problem with the following code :

  filename="inputvideo.mp4"
  
  avconv -i $filename -an -ss 30 test.mp4
  
  avconv -i test.mp4 -vn -ss 30 -i $filename -async 1 testmerged.mp4

  The second line removing the audio of the original video and shifting it 30 seconds (emulating what the opencv-code will do).
  The last line putting the video and original audio (shifted 30 seconds) back together.

  I assumed if I’d both shift them the same amount of seconds, they would be neatly synchronized, but curiously the video and audio in the resulting movie are out of sync. It is a static delay of about about 3 seconds (audio is behind).
  The same problem appears when making an interim mp3 file and using this as audio track for the resulting movie.

  When searching for a solution I found none that resolve this.
  I tried to overcome this issue by using the -vsync/-async options. But since there is no timestamp information in the video this doesn’t solve the problem.
  Even with the latest static build of ffmpeg the audio and video are still out of sync.

  Is there anything I overlooked or is it just impossible to sync audio and video in ffmpeg ?
  And if so, What would be a decent and simple replacement for the funcionality I’m looking for ?