[vdr] FF card AV sync problems, possible fix to VDR (fwd)

Reinhard Nissl rnissl at gmx.de
Wed Feb 21 00:18:31 CET 2007


Hi,

Morfsta wrote:

> OK, so Karsta and I are suffering dropped TS packets. I know for sure
> that my DVB-T signal is not perfect so it is likely to occasionally lose
> some TS packets (freeview in the UK is susceptible to all sorts of
> interference from cars, motorbikes, DECT, etc) however, saying there is
> nothing that we can do about this because you don't have a *perfect* DVB
> signal surely isn't the right answer! My TV copes perfectly well with

Well, what I wanted to say is that I cannot help you any further at this
point. You have to check your hardware/driver whether there is a chance
to minimize packet loss. You did this already as you wrote below -- fine.

> dropped packets and doesn't go out of sync, as does my freeview box.
> Surely if some TS packets are dropped this shouldn't result in a loss of
> sync, the system should resync the audio and continue as before?? It
> can't be right to say, well we lost some data, so we can't recover until
> you change channels up and down, or fastforward/rewind by 1 minute!

You are right -- but don't you think that this thread got a bit off
topic? I've replied in this thread because there were cAudioRepacker
messages and as I've contributed this code to VDR I just wanted to make
sure that it works correctly in this case. Let's now come back to the
topic and concentrate on the AV sync issue.

> I have spent the last 2 weeks trying different combinations, playing
> with my kernel settings, trying USB DVB-T devices rather than the PCI
> and it makes absolutely no difference. The TS continuity errors do not
> go away so I am convinced it is simply that DVB-T is not as robust as
> other signals such as DVB-S or DVB-C. However, VDR should be able to
> cope and resync with lost data.

Well, basically this is not a matter of VDR but of the FF card's
firmware. For example, I do not own a FF card and do not see this AV
sync issue with xine, even when I intentionally drop TS packets by the
attached patch.

I'd like users of FF cards to test this patch. If this triggers AV sync
issues, firmware developers are invited to fix this issue.

Feel free to modify this patch to better simulate real TS packet losses
like bursts of 16 frames.

BE WARNED: *** do not use this patch on a production system ***

Bye.
-- 
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rnissl at gmx.de
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