[mythtv-users] Intermittent MythTV failure

Damian damian at gingermagic.co.uk
Wed Aug 29 11:19:44 UTC 2007

David Watkins wrote:
>> Excuse my ignorance, but I don't know what I'm looking at with logs at
>> the moment. Which bits in particular make you question the dvb card? If
>> I get a feel for what to look for, then I can try the cards one at a
>> time and see if the problems persist.
> It was all this sort of stuff.  I've no idea what it means, but it
> doesn't look healthy and I don't get it in my backend log.
> <snip>
> [dvbsub @ 0xb71ea2e8]Junk in packet
> [dvbsub @ 0xb71ea2e8]Invalid clut depth 0x13!
> [dvbsub @ 0xb71ea2e8]Junk in packet
> [dvbsub @ 0xb71ea2e8]Invalid y position!
> [dvbsub @ 0xb71ea2e8]Invalid object location!
> 2007-08-20 10:58:30.284 AFD Error: Unknown decoding error
> [dvbsub @ 0xb71ea2e8]Junk in packet
> [dvbsub @ 0xb71ea2e8]Invalid y position!
> DVBSub error: line overflow
> DVBSub error: line overflow
> 2007-08-20 10:58:31.713 AFD Error: Unknown decoding error
> [dvbsub @ 0xb71ea2e8]Junk in packet
> [dvbsub @ 0xb71ea2e8]Invalid y position!
> [dvbsub @ 0xb71ea2e8]Invalid object location!
> [dvbsub @ 0xb71ea2e8]Junk in packet
> DVBSub error: line overflow
> [dvbsub @ 0xb71ea2e8]Invalid object location!
> 2007-08-20 10:58:37.190 AFD Error: Unknown decoding error
> 2007-08-20 10:58:40.765 AFD Error: Unknown decoding error
> </snip>

Thanks David, when I get some time I'll try the cards one at a time and 
see it that stuff continues. Has anyone else seen output like this?

>> The other possibility you mentioned is the antenna. I've not got this
>> configured very well at the moment. It's just a standard antenna with a
>> couple of signal boosters. Not great, but it works most of the time so I
>> don't see why that should be causing these intermittent problems.
> What do you mean by a standard antenna?  Most roof antennas designed
> for analog reception work 'sort of' for dvb but may not work well
> enough.  Signal boosters may or may not help depending on where they
> are (If the signal's being lost in the 'noise' then amplifiying both
> doesn't achieve much).  Also it's possible to boost the signal too
> much; some amplifiers have a gain control that you can adjust.

There's an aerial in the loft and two signal boosters downstairs. The 
second of which splits the signal into 4 outputs. I'm using two of them 
to connect directly to my dvb cards.

This is the set up I inherited in this house. I have no idea if the 
previous occupiers used standard terrestrial tv or freeview digital tv. 
Terrestrial is all I have prior experience of before myth.

I assume my set up is not the best it can be, but it works most of the 
time so I've assumed this isn't the cause of the intermittent failures. 
Im more convinced of that by the fact that repeatedly trying to restart 
myth once it's gone fails every time, but logging out and restarting X 
tends to be enough to enable myth to start again. I don't see how that 
could be the case if it was purely a signal problem.

> There's really no subsititute for getting the correct aerial
> professionally installed, but maybe you can fiddle around with what
> you've got to see if you can improve things.  As a rule of thumb you
> want signal boosters as close to the antenna as possible, and you want
> the input to each card to be as identical as possible.  ie don't daisy
> chain them but split the cable into identical feeds.

It would be nice to have an aerial professionally fitted, but I've 
already spend far more on getting myth set up that I originally 
intended. I can't really justify the expense. Especially as I'm not 
convinced that the signal is the 'main' problem.

> The myth log probably isn't the best way to monitor what's going on.
> Do you have a Set Top Box, to see how that performs?  I don't know if
> they produce signal quality stats, but if they do you want to be
> looking for a very low 'bit-error-rate'  (BER).  Actually there's
> probably linux software that will report BER directly from your cards
> (I don't know).

Another new world of lingo :-) anyone know of any Linux apps for this?

> Good Luck
> D

Thanks for your help David!


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