Why does ffmpeg audio volume cmd -af "volume=50dB" not work?

[pxstein]

As far as I understand the following cmd allows me to increase the volume of an *.avi movie (with (lame) mp3 audio)
WITHOUT re-encoding the (embedded) audio track:

ffmpeg -i inputfile.avi -c copy -af "volume=50dB" -y outputfile.avi

After having applied the command to some sample movies I cannot hear any audio volume difference.

Even if I change the command to:

ffmpeg -i inputfile.avi -c copy -af "volume=3" -y outputfile.avi

(which means "make the volume 3 times (!) louder) no difference original vs.result is observable.

Whats wrong?

Peter

[Selur]

Whats wrong?

"-c copy"<> "-vcodec copy -acodec copy"
-> since both audio and video should be copied, no audio and video compression modification takes place.

Only way to boost the volume on playback without reencoding the streams would be to change/add the a Replaygain flags (which are not supported by all players) and since ffmpeg does not support this, you would have to use another tools (mentioned in th link).

[pxstein]

Ok, thank you.

So that means the parameter

-af "volume=50dB"

is only effective when re-encoding audio track?

[Selur]

Yes, audio (and video) filter settings will be ignored if you are not reencoding.

[jagabo]

Try Mp3Gain. It can increase levels without reencoding MP3.

[Selur]

@jagabo: Yes, MP3Gain is one of the tools which are mentioned on the page I linked to, but like I wrote it does not really increase the levels, it only sets some meta data (flags), which are not supported by all players. (especially hardware players)

[pxstein]

The problem with Mp3gain is (afaik) it cannot increase audio tracks INSIDE *.avi videos.

Only separate, stand-alone *.mp3s. But I don't want to de+remux videos.

[Selur]

ffmpeg also would have demuxed and remuxed the file,..
If it's just, that you don't want to do it manually use in example QMP3Gain (https://sourceforge.net/projects/qmp3gain/)