[mythtv-users] Problem Audio on Freeview HD BBC Channels

Glenn Callow gmcallow at gmail.com
Mon May 23 19:34:55 UTC 2011


>> Just a note to say I am seeing the same issue on recordings from BBC HD
>> freeview channel.
>> I get "AFD Error: Unknown audio decoding error" in the logs.
>> I thought clipping the recording after the switch to the main program
>> from the ident would help
>> but does not.

I've reported the bug on the ffmpeg tracker, and one of the ffmpeg devs appears to have recreated the issue.  He's identified it as a problem with the aac decoder, rather than the latm element it seems.  See:


That being said, clipping passed the ident (once the recording has finished) does fix the problem for me when it occurs.  I haven't been clipping inside mythfrontend though.  I'm using dd to snip the first n megabytes off the front of the file, and then place the (slightly truncated) file back in the same place.

If you're clipping in mythtv, it could set the video and audio parameters by looking at the start of the file and that then doesn't fix the problem.

For info I'm using the current atrpms packages for myth 0.24 on Fedora 14.

> Looks like it may not just be Myth experiencing these issues:
> http://www.whathifi.com/news/update-bbc-experiments-with-1080p-broadcasts-on-freeview-hd-but-viewers-complain-of-audio-dropo

Hmm - that's interesting.  The symptoms certainly seem to fit (i.e. the problem occurs at programme transitions between idents).  I haven't checked whether the video format for the problematic sections are different (i.e. 1080i vs 1080p) but I'll have a look.

I've noticed the problem less this last week, but it's certainly still there.  The one thing that pretty much always causes me a problem is the BBC HD ident with the scenes from 'Life' in it (polar bears and penguins).  The scenes look great, but ffmpeg/myth isn't handling the transition in and out of that ident well.


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