[mythtv-users] dtv_multiplex.transmission_mode data type with BBC QAM-256 DVB-T2 streams

[Nemo]

John Pilkington <J.Pilk at tesco.net> wrote:

On 06/02/12 21:44, nemo wrote:

>>> I'm working my way through what's turning out to be a fairly painful
>>> build of a replacement/upgraded server using a Blackgold BGT3650 quad
>>> dvb-t2 card.

> The problem is that the card doesn't seem to switch very well between SD
> & HD (or indeed sometimes between SD muxes). It seems however to work
> better with mplayer if I have a channels.conf that says
> TRANSMISSION_MODE_32K rather than TRANSMISSION_MODE_AUTO and it'd be
> good to make a similar comparison in myth.
>
> At the moment I have it configured with two channel sources - one for
> all the SD channels (3 inputs) and one for the HD ones (1 input). I
> still get too many failed recordings though, but I think that problem
> lies elsewhere.
>
I'm reposting this because the first attempt seems to have vanished. 
Apologies if it arrives in duplicate.

I'm not familiar with this device but I wonder if you have it set up, 
and are using it, to properly take advantage of the multirec feature of 
MythTV.

One HD tuner should be able to record simultaneously, if you wish, from 
all of the HD Channels; no 'Channel switching' is required. Similarly, 
one SD tuner can record simultaneously from more than one channel on a 
selected multiplex. I suspect that the card will be unaware of exactly 
how Myth is dissecting out the channels that you want from the transport 
stream that it provides from a given tuner receiving a single mux.

You set up multirec from the 'Recording Options' screen in the Cards 
section of mythtvsetup; the default number of 'virtual tuners' will 
probably be 2 for each of what you will probably see called 'Adapters'
but I have most of mine set to 4. TTBOMK the disadvantage of using a 
larger number is that scheduling takes longer, and of course you might 
run into disc-throughput problems if you record too enthusiastically.

HTH

John P


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Firstly: my apologies if this top-posts. I don't often use my phone for this type of thing...

Thanks for the suggestion, but I know multirec's not the problem - as part of the debugging process and to prevent individual receivers on the card having to switch between sd and hd streams I've configured two separate input sources. Three tuners (two virtual tuners each) are connected to the sd source and the remaining one (4 virtual tuners) to the hd source. When it works (85%+ of the time) the system quite happily records all 4 hd channels at the same time plus an arbitrary number of sd ones.

Since I'm seeing similar problems when I use (for example) mplayer and also looking at the ubuntu forum thread referenced elsewhere I'm pretty certain that the corrupted recordings I get from time to time are caused by something external to myth. 

All ideas are welcome though.

-- 
Sent from my Android phone with K-9 Mail. Please excuse my brevity.
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