Normalizing audio with ffmpeg

Some videos have really messed up audio, with a globally low volume and/or a very high amplitude between the lowest volume (say, some quiet voice) and the highest (say, some loud music or explosion).

You can analyze the audio track and normalize it directly via ffmpeg, or, more conveniently, with a Python program called ffmpeg-normalize. NB: in case you don’t know about Python, you need to install Python first, then you can run pip. As I’m writing, Python 3.7 works fine with this. Oh, and on a side note, Python is ran by a bunch of sick SJWs so I encourage you to avoid it like the plague and just use it as a last resort.

pip install ffmpeg-normalize
ffmpeg-normalize input.mp4 -tp 0 -vn -c:a aac -b:a 256k -p -o output.mkv

The command as I customized it will skip the video track in the output file and compress in AAC 256kbps, which is most likely too much. I do that because I actually want to re-encode the audio properly afterwards: I use Opus (libopus) and ffmpeg-normalize doesn’t support all the Opus options I want to use. So then I would run for instance:

ffmpeg -i output.mkv -ac 2 -codec:a libopus -b:a 64k -vbr on -compression_level 10 -frame_duration 60 -application audio output2.mkv

If you just want to analyze a file:

ffmpeg -i input.mp4 -filter:a volumedetect -f null /dev/null

or on Windows, using NUL:

ffmpeg -i input.mp4 -filter:a volumedetect -f null NUL