[mythtv-users] HDTV digital static with DVB

[Chris Trown]

Preston Crow wrote:
> On Tue, 2005-11-08 at 17:14 +1000, ffrr wrote:
> 
>>I chased video glitches from my DVB setup for ages, and with a lot of 
>>help from the list, I finally nailed it.  It was the Si 3112  SATA 
>>controller chip doing nasties on the PCI bus and corrupting the mpeg 
>>stream from the DVB card.
>>
>>This would correlate with your observation that it is worse with system 
>>load, in particular disk access.
> 
> 
> I have two hard drives.  If I simply cat /dev/dvb/adapter0/dvr0 to a
> file on the SATA drive, I get some glitches.  If I do the same to a file
> on the PATA drive, I get tons of glitches.  If I do it to a ram disk, I
> get a perfect recording.
> 
> So it doesn't look like it's the SATA chipset doing something nasty.  In
> fact, the SATA drive, being on a faster bus, gives me a better recording
> than the PATA drive.  This makes it look more like my original theory of
> being an issue that can be solved in the DVB driver.  Of course, it
> could be the SATA chipset or anything else on the PCI bus, but if
> something were corrupting the DVB traffic, wouldn't it also corrupt
> other traffic, like disk I/O?
> 
> Instead of it being a kernel buffer that is too small, perhaps it is too
> slow to pull the data off of the card?
> 


      This thread has me wondering, now.  I just got MythTV going and 
have done some test records.

      The Simpsons Halloween special recorded just fine, but it was in 
SD format(Recorded from the HD channel).  That same night, I tried to 
record Law & Order:CI.  That recording had a lot of breakups and qudio 
dropouts.

      The system is a 3.06GHz P4 with a HD3000 and a Rosewill Nvidia 5200FX.

      My understanding is that recording DVB streams is not CPU 
intensive.  The card just grabs the digital data off the air and the 
system writes it to disk for later manipulation/transcoding.  Am I 
correct?  If that is true, then I am casting a suspicious eye to 
problems with reception.  I know that there is one channel that MythTV's 
scan didn't pick up.

      So I guess my question, is how can I tell if the problem I'm 
seeing is trouble with recption vs. a possible system throughput issue?

Chris...

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