[mythtv-users] Mytharchive DVD creation: sound loss part-way through a recording

John Pilkington J.Pilk at tesco.net
Tue Nov 10 00:29:27 UTC 2009

Gavin Peters wrote:
> On Mon, Oct 26, 2009 at 09:56:13PM +0000, John Pilkington wrote:
>> I routinely archive DVB recordings to DVD.  Under 0.21-fixes recently  
>> this rarely failed, but during the past week, under 0.22 fixes, the  
>> sound on two films has vanished part-way through the conversion.  The  
>> original recordings played well. Here are short sections of the 516KB  
>> mythburn.log
> John,
> Did you ever find out what was causing your DVD archiving trauma?  If you solved it I'm
> interested to hear how.
> - Gavin

I haven't found any cause, or a cure yet, although ProjectX has been 
recommended.  I remember one instance with 0.21 and hope there weren't 
more that I haven't noticed yet because I haven't played the DVDs; with 
0.22 it's happening too often for comfort.  A few of the instances could 
perhaps be due to interference, with a brief AV disturbance, but on the 
DVD the audio loss is permanent.

The main problem seems to be an inability to recover from a single 
instance of 'wrong audio frame size'.  Mythreplex reports that it 
happens, and mplex reports that 'data follows the last recognised audio 
frame - bad stream?' but no effective remedial action is taken - whereas 
  the player apparently takes it in its stride.  Action as early as 
possible in the chain would be best.  The bad sections pass through both 
mythtranscode and mencoder, as I currently use them, without comment or 
correction.  I stopped re-encoding from mp2 to ac3 several months ago, 
because it seemed pointless, but I suppose that that might have 
sidestepped some other code.

I've made DVDs from a few of the affected recordings by editing out the 
bad section - usually about 3 seconds seems enough - using 'mythfrontend 
-v audio' to find first the end, and then the start, of the glitch after 
noting when the sound vanishes from the DVD, but this is *very* cumbersome.

John P

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