[mythtv] Re: Australia DVB playing problem...

[Marek Musial]

July 18, 2005, sammo2828 wrote:
> 2. Bad reception, or RF noise/interference (e.g. light switch, fridge
> turning on/off, etc) corrupts DVB stream. Sometimes this stuffs up audio for
> both live tv and recorded shows. 

I have spent some effort to isolate this audio-loss problem. I am using DVB-T 
in Berlin, Germany, Myth from svn some time after the 18.1 release and a 
Medion 7134 combo card (saa7134-dvb). 

I have also been getting occasional spontaneous audio losses in PS mode in 
both LiveTV and recordings, about once every hour, at least on the channels 
SAT.1 and RTL (both with a single and with two audio streams, by the way). I 
found out that DVBRecorder::ReadFromDMX() continues to issue occasional (~ 
every 2 minutes) "Stream Continuity Errors" on ALL pids that have been 
selected for recording, INCLUDING the audio stream that has broken! This 
means that DVBRecorder::ReadFromDMX() still gets data from the card for the 
affected stream. However, having added some additional debug messages, I 
found out that DVBRecorder::LocalProcessDataPS() is no longer calling 
ringBuffer->Write() for the lost audio stream (which is quite a good reason 
for it being lost, actually...). On the other hand, some (very limited, 
though) testing indicates that I do not get these audio losses with TS 
recording.

Conclusion: There seems to be some issue within the transcode.c infrastructure 
(instant_repack(), send_ipack()) for rebuilding the stream, which is bypassed 
in TS mode. It is beyond my qualification to find out what exactly 
transcode.c is doing wrong...

> Changing from PS to TS also has no effect because I find that myth ALWAYS
> records all audio tracks.

Hmmm, while the latter is definitely true, it might not actually be a reason 
for the changing to have no effect. For the data processing (from 
DVBRecorder::ReadFromDMX() on) is completely different for TS vs. PS modes. 
Have you ACTUALLY experienced spontaneous audio losses (your "class 2") in TS 
mode as well??

Hope this helps,
Marek