amultiply

doc

https://ffmpeg.org/ffmpeg-filters.html#amultiply

see also

aeval, aevalsrc

This filter does multiply first audio stream with second audio stream and store result in output audio stream. This is not available on ffmpeg 3.x.

[me@host: ~]$ "/c/Program Files/ffmpeg-4.1-win64-shared/bin/ffmpeg" \
> -filter_complex "
> aevalsrc='sin(t*2)|cos(t*2):d=30'[a1];
> amovie=some.wav[a2];
> [a1][a2]amultiply" -f wav - | ffplay - 2>/dev/null

In this case, the same can be achieved with “aeval”:

[me@host: ~]$ ffmpeg -filter_complex "
> amovie=some.wav
> , aeval='sin(t*2)*val(0)|cos(t*2)*val(1)'" -f wav - | ffplay - 2>/dev/null
[me@host: ~]$ ffplay -f lavfi "
> amovie=some.wav
> , aeval='sin(t*2)*val(0)|cos(t*2)*val(1)'"