[mythtv] DVB-C and MythTV

Rudy Zijlstra mythtv at grumpydevil.homelinux.org
Sat Jun 2 11:51:42 UTC 2007

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.

> 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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