ffmpeg example template for audio fft processing #filtergraph #batch

fft.sh

#!/bin/bash
# the following mixes 2 FFT-expressions into a dry (FFT) signal
set -e
in=/tmp/somefile.wav
out="$in.ffmpeg.wav"
winsize=1024
fft_a_r="real='0'"
fft_a_i="imag='tanh(re / 8) * lt(b,4)"                     # bins 0-4
fft_b_r="real='0'"
fft_b_i="imag='tanh(re * 1.8) * gt(b,150) * lt(b,512)'"    # bins 150-512

filter='channelsplit=channel_layout=stereo [aL][aR];
[aL] asplit=outputs=3 [as1L] [as2L] [as3L];
[aR] asplit=outputs=3 [as1R] [as2R] [as3R];
[as1L] afftfilt=overlap=0.9:win_size='$winsize':real=re*1:imag=im*1 [as1LFFT];
[as1R] afftfilt=overlap=0.9:win_size='$winsize':real=re*1:imag=im*1 [as1RFFT];
[as2L] afftfilt=overlap=0.9:win_size='$winsize':'$fft_a_r':'$fft_a_i' [as2LFFT];
[as2R] afftfilt=overlap=0.9:win_size='$winsize':'$fft_a_r':'$fft_a_i' [as2RFFT];
[as3L] afftfilt=overlap=0.9:win_size='$winsize':'$fft_b_r':'$fft_b_i' [as3LFFT];
[as3R] afftfilt=overlap=0.9:win_size='$winsize':'$fft_b_r':'$fft_b_i' [as3RFFT];
[as1LFFT][as1RFFT] join=inputs=2:channel_layout=stereo [out1];
[as2LFFT][as2RFFT] join=inputs=2:channel_layout=stereo [out2];
[as3LFFT][as3RFFT] join=inputs=2:channel_layout=stereo [out3];
[out1][out2][out3] amix=inputs=3,volumedetect
'
timeout 2s ffplay -i "$in" 
set -x
ffmpeg -i "$in" -af "$(echo "$filter" | tr -d '\n')" -ac 2 -y "$out"
timeout 2s ffplay -i "$out"