[mythtv-users] Ignoring certain channels from certain inputs

Karl Dietz dekarl at spaetfruehstuecken.org
Sun Oct 21 09:32:37 UTC 2012


On 21.10.2012 01:37, Jean-Yves Avenard wrote:
> Hi
>
> On Sunday, 21 October 2012, Mark Greenwood wrote:
>
>
>     In the UK, DVB signals include channel numbers, so by 'sensible' I
>     mean 'following the channel order as defined in the signal'. Mythtv
>     appears to ignore this. A rescan on my myth box takes 15 minutes,
>     then I have at least 2 copies of each channel so I have to work out
>     which one is the best for each channel then set a channel number and
>     delete the others. But then because I've set my own channel numbers
>     but myth invents new ones when I rescan (e.g. 4283 for BBC1..huh?) I
>     get loads of duplicates as well. It's a nightmare. It also doesn't
>     take account of the signal strengths of the channels it finds,
>     whereas my TV will choose the best signal for each channel and
>     discard any duplicates, hence I only get one BBC1 and it's on
>     Channel 1, instead of 3 of them randomly distributed across the
>     channels like I get with mythtv. (The first scan, I had BBC1 on
>     channels 1, 46, and 4283. Where did it get those numbers from? The
>     only one that gives a decent picture is the one on 4283 so it sho
>       uld have chosen that one and thrown the other 2 away).
>
>
> Myth uses the channel as defined by the DVB stream. It may not be what
> you're used to, but that's what the broadcast uses.
>
>
> In Oz, after a scan, channel 9 is on 9, Seven on 7, Ten on 10 etc..

In the UK you'll get duplicates if you can receive multiple networks
(aka transmitters carrying the same channels). You'll get random
channels if you get the same transport (as identified via
original_network_id and transport_id) is received on multiple
frequencies. That's a known error that I've seen on german DVB-T.
Yes, the proper way is collecting them all and picking one of them by
default, maybe depending on bit error rate or signal strength (up to
the implementer)

The easiest work around is to not perform a full spectrum scan but
instead start on a known frequency of one of the networks/transmitter
sites and letting the scanner learn the related frequencies from the
network_information_table.
You should only get one copy of each channel that way.

I was sure that the channel scanner supports the logical_channel_number
transmitted in the network_information_table (1 for BBC1 in your
example) but I can't find any evidence in the code right now.
The 4283 is coming from the service_id that is used to refer to this
service in other DVB tables. I've no idea where the 46 is coming from.
(the logical_channel_number is what got shuffled around lately
http://en.wikipedia.org/wiki/List_of_digital_terrestrial_television_channels_(UK) 
)

Once you have that scan done you can run 
http://www.mythtv.org/wiki/UK_Channel_Assignments to connect to the 
channel_ids from tv_grab_uk_rt

Regards,
Karl


More information about the mythtv-users mailing list