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
avconv -i in.mts -an -c:a copy video.mkv -c:a copy audio.ac3
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
avconv -i video.mkv -i audio.oga -c:v copy -c:a copy out.mkv
- Video was getting copied all the time. So no quality loss is possible from that.
- You can drop the video demuxing, and just grab it directly from the original in the third step. But i find it just makes the process much cleaner when you know where everything is.