[mythtv] DVB Stability problems with watching live TV

Mark Howells Mark.Howells at softoption.com
Mon Aug 9 06:07:28 EDT 2004

> -----Original Message-----
> From: Damian Ivereigh [mailto:damian at cisco.com] 
> Sent: 09 August 2004 10:12

> Has anyone else experienced stability/crashing problems when 
> watching Live-TV with DVB cards?

Yes.  I've posted on this issue a couple of times. A trip through the archives will reveal a number of posts from other users.  

> I have been using mythtv with a couple of Australian Nova-T 
> DVB cards for the last few months. The recording and playback 
> works great, rock solid.

Same for me.

> However I have found a couple of wierd problems when watching 
> live TV:-
> 1) When switching channels, sometimes the player never gets 
> up to speed, staying at that slow speed it uses when trying 
> to get the video and audio in sync.

Again, same for me.  Generically, this is symptomatic of the backend server suffering from TS continuity errors.  I'm certain that, in my case at least, the card itself isn't reporting errors as

1. The problem only exists in mythtv
2. When this happens, stopping and starti8ng the backend fixes the problem.

I'm fairly certain there's some kind of bug in the tuning code for Mythtv but I've been hunting through the source code for a while now and can't see anything suspicious (yet).  I'm reasonably certain that it's not a hardware / PCI / antenna problem as the card produces a fine data stream when running under other environments.  

However, I have trialled different PCI latency settings, moved the card to a dedicated IRQ PCI slot and checked the antenna against a STB (which works perfectly)

Furthermore, changing channels within the same MUX doesn't seem to cause the problem - it only seems to manifest itself when performing an actual tuning operation. More evidence that it's a fault in the way mythtv interacts with the DVB drivers (or a possible fault in the DVB drivers I suppose).

> 2) When the signal quality is a bit flaky (and the card 
> temporarily loses sync), I have seen both the front and 
> backend crash (at different times). I realise that the 
> solution is to fix the signal quality, but I would prefer 
> myth to handle this situation a bit better.

Again, there have been one or two posts discussing what could be done.  Rather than crashing (obviously) I would prefer a message screen stating that "stream is out of sync - resynching" or somesuch.

> I am not looking for a fix (unless someone has one), rather 
> to know if anyone else has experienced it. If so I will have 
> a go at debugging and fixing it.

I did look at this a while ago, but haven't had the chance recently to do anything recently.  I'm away on hoiday soon for a couple of weeks but when I get back, I'll have a bit more time.


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