[mythtv] DVB-C and MythTV

Christiaan van Dijk dvbmail at xs4all.nl
Sat Jun 2 11:57:38 UTC 2007



Rudy Zijlstra wrote:
> Christiaan van Dijk wrote:
>   
>> Hi all,
>>
>> I've been working on a MythTV box with a DVB-C card and ran into some 
>> problems. I solved quite some issues and would like to share these here.
>>
>> A known problem with DVB-C are the network IDs. In a normal DVB 
>> situation there's only one main network ID in the NIT which describes 
>> the used network. In DVB-C however the network ID needs to be entered 
>> manually and is not even located in the NIT but in NITo. I've seen 
>> some discussion on how to deal with this since it's not really DVB 
>> standard and solutions are mainly dirty hacks which only pollute the 
>> code. I tried a solution which is a bit in between (to my opinion :-) 
>> ), this solution makes it possible to give a network ID in the 
>> configuration script which is compiled into the code, if not defined 
>> (default) the code stays in it's original state. There is some code 
>> pollution with the conditional defines but I tried to keep it to a 
>> minimum.
>> To use a fixed network ID simply add the option --dvb-net-id=1111 to 
>> the configuration script (for network ID 1111).
>>     
>
> Do not know the code in question, but do know one other thing to keep in 
> mind. All @home networks use the same original_networkID.  And it is the 
> original_networkID that is stored in the netwrokid column of dtv_multiplex.
>
> I am not aware of any place where the network_id is stored!
>
> Hope you covered this as well.
>
> Rudy
>   
The network ID is only needed when scanning for channels. The matching 
NITs provide information on which channels/carriers are available. The 
found channels are stored with the original network ID as reference. The 
original network ID is also used in the EIT fixup part. Quite nice since 
this fixes all AtHome options at once instead of having to add every 
network ID (1111/5555/7271/9004/9003/9001.....).  It might be a bit 
confusing to see the network ID set to 1000 (original) while scanning on 
1111 (in my case).

Christiaan.
>> There still is a bug in the standard code for handling the NITo 
>> tables, the buffering of the different sections needs to take the 
>> network ID into account since the NITo tables can and will include 
>> multiple network IDs. This could be tricky since there could be up to 
>> 64k-1 IDs in theory. The patch avoids this problem by only 
>> interpreting the NITo/NIT with the matching network ID as main NIT.
>>
>> Also fixed a bug in the channel inversion setting, the scanner used to 
>> set an invalid value for DVB-C, now it defaults to auto. Really minor 
>> but avoids warnings in the log files.
>>
>> When scanning for channels first enter one transport manually, scan 
>> the transport, all available transports will be added and do a final 
>> scan to get all the channels. Did not look into a fix for this yet 
>> since it's a pretty simple action.
>>
>> Second problem part lies in the program guide. The cable company here 
>> (AtHome, Netherlands) uses a different interpretation of the short and 
>> extended EIT tables. The description always starts in the short 
>> description tables and continues in the extended table, there is no 
>> sub-title information. I added a fix for this in the EIT code part, 
>> tried to do it as much as possible in line with the other EIT fixups 
>> but it's a little tricky since it's both early/normal fix. The code 
>> tries to extract the episode information first from the description 
>> and if this fails from the main title. Not perfect but works for me 
>> and now I can record a series without having to select each episode or 
>> define a special recording rule. Also the descriptions are now complete.
>>
>> I did comment out the UK channel numbering part since this screws up 
>> the channel numbering here. No big issue but it confused me a bit in 
>> the beginning. Cable box seems to get the channel numbers in another 
>> way, did not figure this one out yet.
>>
>> Well, that's it for now. Still working on some other issues but the 
>> weather is way too nice to sit behind the computer all day :-) . Main 
>> problem remaining is the starting of live TV, sometimes the DVB stream 
>> will not start or takes too long and myth returns with an error, did 
>> not see this in normal recordings.
>>
>> All the patches are attached, I hope this helps other people fighting 
>> with DVB-C boxes. Good luck!!!
>>
>> Regds,
>> Christiaan van Dijk
>>     
>
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