Adjust volume level
audio
// what it does
Scales the audio gain with the volume filter, which is a plain sample multiplier: 2.0 doubles amplitude (+6 dB) and 0.5 halves it (-6 dB). You can also write it in decibels like volume=6dB. Applying -af forces the audio to be re-encoded, so pair it with an appropriate -c:a if the default isn't what you want.
// shell
$ ffmpeg -i input.mp4 -af "volume=2.0" output.mp4$ ffmpeg -i input.mp4 -af "volume=0.5" output.mp4// gotcha
volume is a raw multiplier with no limiter, so boosting a signal that already peaks near 0 dBFS clips and distorts; normalize or use loudnorm instead of blindly multiplying.