I can do audio phase subtraction in Adobe Audition like so:

How can I do this with FFmpeg? Is it possible?

I've googled for audio phase subtraction, and looked at https://ffmpeg.org/ffmpeg-filters.html, nothing seems to work for me.

I want to do phase subtraction in batches and support for stereo audio.

  • 1
    You can do this in something like Audacity, but why the need for batch processing? It's the kind of thing that only works if you have absolute phase-alignment to start with*. I struggle to see a use case you would have multiple examples of this type of overlay with identical start-points/phase alignment. It makes the whole question feel like a bit of an XY Problem *[I didn't watch the whole thing, but did the guy tell you it took him 20 minutes to phase-align his example before he started the video?]
    – Tetsujin
    Apr 22, 2023 at 17:26
  • 1
    See the aeval filter.
    – Gyan
    Apr 22, 2023 at 19:01
  • 1
    @tetsujin I want to compare audio compression using different codecs, with perfectly aligned audio files. Additionally, I want to compare audio encoding across various scenarios, which is why I need to perform this task in batches.
    – Calarpo
    Apr 23, 2023 at 4:08

1 Answer 1


I have found a solution:

ffmpeg -i input0.wav -i input1.wav \
  -filter_complex \
  "[1]    aeval  = -val(0) | -val(1)                     [a]; \
   [0][a] amerge = inputs=2,pan=stereo|c0<c0+c2|c1<c1+c3 [b]" \
  -map "[b]" -c:a flac output.flac

This command subtracts input1.wav from input0.wav and assumes that both inputs are stereo.

See https://trac.ffmpeg.org/wiki/AudioChannelManipulation for manipulating audio channels.

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