Do you know how I can, or if there is a programme that can, change the audio format in a video file without interfering with the video compression? For example, I want to change a video in MKV format that has 6 channel audio to stereo without changing the video compression.






Try Video Toolkit 2 - set the video compression to "copy", change the audio compression to "stereo" and whichever codec you want.
Not sure which issue cover disc it was on but I think it was on the May 2011 issue cover disc.
Cheers, Darren.