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• Concatenation of files using ffmpeg does not work as I expected. Why ?

  19 décembre 2018, par Peter Olson

  I execute the following command line

  ffmpeg.exe
  
      -i C:\Beema\video-source\DO_U_BEEMA176x144short.avi 
  
      -i C:\Beema\video-source\DO_U_BEEMA176x144short.avi 
  
      -i C:\Beema\temp\9016730-51056331-stitcheds.avi  
  
      -i C:\Beema\video-source\GOTTA_BEEMA176x144short.avi 
  
      -y -ac 1 -r 24 -b 25K 
  
      C:\Beema\video-out\9a062fb6-d448-48fe-b006-a85d51adf8a1.mpg

  The output file in video-out ends up having a single copy of DO_U_BEEMA. I do not understand why ffmpeg is not concatenating.

  Any help is dramatically appreciated,

• How the ffmpeg astats crest factor value of an audio track is calculated

  29 août 2017, par FranGar

  I’m scripting a ffmpeg chain process for my work. The aim is normalizing/compressing lot of audio files (mp3’s).
  It’s done in Python and the critical part is the line :

  ffmpeg -y -i "Input.mp3" -codec:a libmp3lame -b:a 96k -af acompressor=threshold=-15dB:ratio=5:attack=0.01:release=1000:knee=2,dynaudnorm=g=3:m=2:p=0.95 "Output.mp3"

  The python script it’s complete and working BUT the nature of the audios (voice recordings) are very different so I can’t use the same params for all of them.

  I make some experimenting with the values of the ffmpeg filter astats and i discovered that the crest factor (Standard ratio of peak to RMS level ) gave a good reference to programatically get the better params.

  In fact I saw that a recording with a nice dynamic range sound and smooth in shape, get crest values around 9-15 (the compress/normlz params will be somehow conservative). But audios with crest around 22-30 need more aggressive processing.
  (All empirically)

  Somebody can clarify how the crest values are really calculated ? Which are the peaks taken to account ? (Why the flat factor is always 0 ?)
  Or if somebody knows how to get a value representing the sound ’smoothness’ will be nice also.

  Thanks for the ideas.

• How the ffmpeg astats crest factor of an audio track is calculated

  29 août 2017, par FranGar

  I’m scripting a ffmpeg chain process for my work. The aim is normalizing/compressing lot of audio files (mp3’s).
  It’s done in Python and the critical part is the line :

  ffmpeg -y -i "Input.mp3" -codec:a libmp3lame -b:a 96k -af acompressor=threshold=-15dB:ratio=5:attack=0.01:release=1000:knee=2,dynaudnorm=g=3:m=2:p=0.95 "Output.mp3"

  The python script it’s complete and working BUT the nature of the audios (voice recordings) are very different so I can’t use the same params for all of them.

  I make some experimenting with the values of the ffmpeg filter astats and i discovered that the crest factor (Standard ratio of peak to RMS level ) gave a good reference to programatically get the better params.

  In fact I saw that a recording with a nice dynamic range sound and smooth in shape, get crest values around 9-15 (the compress/normlz params will be somehow conservative). But audios with crest around 22-30 need more aggressive processing.
  (All empirically)

  Somebody can clarify how the crest values are really calculated ? Which are the peaks taken to account ? (Why the flat factor is always 0 ?)
  Or if somebody knows how to get a value representing the sound ’smoothness’ will be nice also.

  Thanks for the ideas.