[FFmpeg-user] Enable all audio channels

[MI]

> I have tried using QT Pro to set all tracks (enabled) and while this works for
> other QT files, it doesn't seem to work with the files I'm creating with ffmpeg -
> after saving, closing and re-opening the QT files, the tracks are disabled again.

Yes, I also noticed this, but didn't do further tests since I wanted to have ffmpeg 
enable them anyway, without needing to go through QT Pro.

On similar files (Prores/8 mono audio tracks) produced with Final Cut capture, QT Pro 
lets me enable all tracks.

> However, once the QT files are imported into an editing system, all eight tracks
> seem to be present and accounted for - but I'm still testing.

Maybe this "enabled" flag is really not important and the important thing is how to 
label/assign the tracks so that people further down the chain know which track is which.