[popcornmix]

OK - I waited for the current build ( helix ) to drift which it did after about an hour this time.
The drift was very noticeable.
Quickly recorded the channel for ten minutes, and then played it back.
Surprise, surprise, when playing back the recorded clip, IT WAS IN PERFECT SYNC!

Does that help?

My understanding is that a "corrupt" packet puts the audio out of sync.
Recording after the sync has gone wrong is too late (it's just like stopping and restarting live tv - it will be back in sync).
The recording needs to start when video is in sync, and catch the point where sync gets broken.
Hopefully the file will then repeatably go out of sync at the same point each time it is played and can be debugged.