#285 pipe decoded audio from ffmpeg to sox
I use sox to generate spectrogram images automatically over plenty of audio files. As sox does not support m4a files I decode these files usinf ffmpeg and pipe them into sox.
My command line is:
"C:\Program Files\ffmpeg-20161217-d8b9bef-win64-shared\bin\ffmpeg.exe" -y -i "my_music.m4a" -f sox - | "d:\down\Programme\sox-14.4.2\sox.exe" -p -n spectrogram -w Hann -o my_music.m4a.png
This results in the generation of a spectrogram image that reports a playtime of the music of about 8 seconds. My m4a file has a duration of a few minutes.
If I alter the command line to have ffmpeg deliver wav, sox eventually reports:
WARN wav: Premature EOF on .wav input file
Modified Command is:
"C:\Program Files\ffmpeg-20161217-d8b9bef-win64-shared\bin\ffmpeg.exe" -y -i "my_music.m4a" -f wav - | "d:\down\Programme\sox-14.4.2\sox.exe" -t wav - -n spectrogram -w Hann -o my_music.m4a.png
As this command results in a working wav file I think sox does not read the pipe correctly.
"C:\Program Files\ffmpeg-20161217-d8b9bef-win64-shared\bin\ffmpeg.exe" -y -i "my_music.m4a" -f wav - >my_music.wav
What is the best way to pipe audio decoded by ffmpeg to sox?
The spectrogram generator needs to know the length upfront in order to scale the image correctly. If the length is unknown, it arbitrarily uses the first 8 seconds. You can either decode to a temporary file or extract the length by other means and pass it to the spectrogram effect using the -d option.