[mythtv-users] Ignoring certain channels from certain inputs

[Mark Greenwood]

Thanks all for your informative responses. My TV is a Panasonic and has always tuned itself perfectly wherever I've lived.

I appreciate you all taking the time to post this info, trouble is you've all assumed I have qualifications in broadcast technology. 

For example:

> Select the transports that match your "good" transmitter and do a "Scan existing transports" instead of a full scan

What are transports? How do I know which transports match my good transmitter? Where do I go to select the transports once I've found out? Why do I even need to know all this when Panasonic can make a TV that does it all for me?

I appreciate that mythtv is international and that what works here won't work anywhere else, but I still think it'd be worth giving it a go because over the years I've been using it I've come to feel a sense of terror whenever I think something might need reconfiguring :)

Mark

On 21 Oct 2012, at 10:32, Karl Dietz wrote:

> 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
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