[FFmpeg-user] isolate 'voices', move them, and mix into another audio stream

[Mark Filipak]

I have two ac3 audio streams. One is 'voices+noise', the other is just 'noise' -- no voices. I want 
to take 'voices+noise', remove 'noise' leaving just 'voices', then mix 'voices' into a latter, 
clipped version, call it 'sounds'. I could do it with Audacity, but I'd like to do it with FFmpeg, 
if possible.

I seek experienced guidance because I've never done this before and I want to use the best audio 
mixer 'filter' available -- knowing what's best comes only via experience.

The full story:

"2001, A SPACE ODYSSEY" has a tedious, 2:58.136 prelude that is just 'noise', after which the MGM 
Lion appears. When I made an mp4, I cut 'm2ts 0..178.136' out leaving just 'm2ts 178.136...', which 
is now 'mp4 0...', which begins with the MGM Lion.

When I finished, I discovered that in their comments track, Keir Dullea and Gary Lockwood introduce 
themselves during that 'noise'. Their 'voices' spans 'm2ts 0..34.034'.

I want to take 'm2ts 0..34.034', remove the 'noise' so that only 'voices' is left, then mix 'voices' 
into 'mp4 0..34.034', over the MGM Lion. There's a little more clipping and joining to be done but I 
can handle that.