[mythtvnz] Losing sound when processing mpg files

[Scott Newton]

Generally I process any MythTV files on my local computer rather than using 
Myth Archive as I find it easier. After searching the web I have come up with 
the following process which I use to process the files:
1. Run the file throught projectx.sh -demux to resync the video and audio.
2. Run mplex -f 8 over the output files from 1 to put them back together 
again.
3. Use Avidemux 2.4.4 to edit the file and produce the final output file using 
DVD(lavac - two pass - video size) for Video and Copy for Audio .

However, on the odd occasion, the output file from avidemux will lose the 
sound at one of the edit points and the rest of the file from there on will be 
silent.  

I have three questions which if anyone knows the answer would be much 
appreciated:
1. Why does this happen?
2. How do I get around it?
3. Is there a better way?

Thanks
-- 
Regards
Scott Newton