[mythtv] DVB Stability problems with watching live TV

Damian Ivereigh damian at cisco.com
Mon Aug 9 09:38:02 EDT 2004

On Mon, 2004-08-09 at 20:07, Mark Howells wrote:

> > 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.

Actually I just have to Escape out and re-select "Watch TV" - i.e.
restart the player part of the frontend, which I presume causes the back
end to have another go a resyncing with the signal.

> 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.  

Totally agreed.

> 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'll go and find them.

> > 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.

Well I can provide some great test cases for you. I have set this same 
system up for several of my friends all with different signal strengths.
I will have a dig around myself.

Thanks for the reply,

Damian Ivereigh
CEPS Team Lead
Desk: +61 2 8446 6344
Mob: +61 418 217 582

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