[mythtv-users] no sound after mythtranscode

[Mike Parkins]

After transcoding Carole King on BBC4 to tidy up the start/end for 
posterity, I played it and got no sound. Finding the audio selection 
menu I noticed it set to "English MP2 1ch" with a 2ch option below. 
Selecting the 2ch option gave me back my sound. Un-transcoded programs 
seem to vary in whether the audio track selection menu appears or not. 
An episode of 'Click' from BBC News24 had no menu. Doctor Who had two 
options...

1:English MP2 2ch
2:English MP0 ?ch

What is going on here?