[mythtv-users] Ignoring certain channels from certain inputs
Mark Greenwood
fatgerman at gmail.com
Sun Oct 21 11:08:11 UTC 2012
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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