is there any program to increase the volume of a video file without having to demux it and re-encode it?
or what is the best program to demux and remux files?
I have used mp3gain in the past for mp3 files but cannot find anything for video files.
AviDemux can work without demuxing. Video can be set to 'Copy' but to change the audio level you'll have to re-encode the audio. You don't say what format the original is in, but since it has lots of built in CoDecs it will probably have the ones you need.
Mpeg DVD Wizard.