I've got a large amount of .MKV video files which seem to all play at a very low volume - I end up having to turn the TV up all the way to hear them, which is really irritating when I switch to another channel and wake the dead because it's so loud.

What I'm looking for is a command-line method to increase the volume (so I can run it on all of them quickly) that would hopefully work regardless of the audio codec in use in the particular file. (I don't mind hard-coding the output audio though).

For reference, I'm using Ubuntu 9.04 on my server, and the files are being played back with Boxee on a Mac Mini, but the volume problem is the same on Windows too.