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Using ffmpeg's audio compressor/expander

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Chiq Garcia
Using ffmpeg's audio compressor/expander
on Nov 14, 2013 at 3:57:41 am
Last Edited By Chiq Garcia on Nov 14, 2013 at 6:16:24 am

I would like to share my personal remedy for videos/movies with barely audible 'whisper dialogues' followed by deafening explosions. While there is no one-size-fits-all setting for compression, I am hoping that this at least points you in the right direction or that you find it practical.

example (stereo):
"C:\ffmpeg.exe" -i "C:\InputVideo.mp4" -vf "scale=512:384, setsar=1" -af "compand=0 0:1 1:-90/-900 -70/-70 -21/-21 0/-15:0.01:12:0:0" -c:v libxvid -b:v 800k -r 24 -c:a libmp3lame -b:a 128k -ar 48000 -ac 2 "C:\OutputVideo.avi"

translation:
audio filter, compand, attack 0, release 1, -90 db in/inf out (gate), -70 db in/out, -21 dB in/out, 0 dB in, -15 dB out, soft knee default 0.01, 12 dB makeup gain, input level 0 dB, lookahead 0. Nasty transients seem to 'escape' the compressor if you omit "-90/-900" (I don't know why).

If this functionality had a GUI, it would probably resemble Adobe Audition's dynamics processing (comes with a graph).

Learning audio compression is tricky, and I found myself learning it and then re-learning it a couple more times. I guess it would be a dream come true if ffmpeg supported VST plugins like tube-saturation/brickwall limiting (e.g. Ferric TDS).

For a convenient ffmpeg GUI, google: "en masse, batch processor for videos" and follow the yo*tub* link.

En Masse ~ batch processor for videos






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stephen dixon
Re: Using ffmpeg's audio compressor/expander
on Nov 14, 2013 at 11:26:44 am

Thanks for the tute. For a slightly more user friendly command line audio processor try sox. I usually extract audio, process in sox and remux.

Stephen Dixon
Editor, Animator, Motionographer
Museum Victoria


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