I need just increase sound of my MTS video. But I'm very afraid to lose the quality of video because it is classical music and intonation is very important.
The setup that i use for something similar is:
Step 1 - demux
Step 2 - audio editing
For this i just open my audio.ac3 in Audacity and normalise the sound. At this time it may be a good idea to try to remove the noise. I reencode into Vorbis, but it is up to you what you wish to do. Let's say you save into audio.oga
Step 3 - mux