[mythtv] Adding PLP support (DTV_STREAM_ID)

[Peter Bennett]

On 01/28/2018 08:12 AM, Torbjorn Jansson wrote:
> Hello.
>
> i have a few questions but first some background.
>
> several years ago i bought a usb based dvbt2 tuner with the intention 
> to replace my pcie card.
> i picked a TT CT2-4650 since it was supposed to have linux support 
> already.
> turned out that was not true since i got a newer version of it with no 
> linux support, so with a bit of hacking on the drivers i was able to 
> get it working due to the similarities with other cards.
>
> but i quickly realized i could not tune to any dvb-t2 mux, after a lot 
> of troubleshooting i gave up and forgot about it.
>
> then a year or so later my dvb tv box broke down and i bought a new 
> one (vu+ solo4k) and to my surprise it had the exact same issue.
> after even more troubleshooting i found out i need to set PLP ID to 1 
> for tuning to work on dvb-t2 muxes.
>
> so then i realized that must be the same problem with my ct2-4650 and 
> it was.
> yesterday i got tvheadend working on the usb tuner successfully and 
> thats the first time i got the usb tuner to do something useful.
>
> BUT channel scanning is not working, so mux must be setup manualy, 
> that includes PLP ID and other paramters.
> so i think the drivers don't do auto detect like my pcie card does.
> and the downside of missing autodetect of plp is that most software 
> dont know how to handle plp and this applies to mythtv too.
>
>
>
> so for mythtv to work with this card i need to convince the backend to 
> specify plp when tuning.
> so a new mux paramter need to be added to database and then used 
> during tuning.
> as i understand it this is done with a property called: DTV_STREAM_ID 
> and i need to try to understand better how 
> libs/libmythtv/recorders/dvbchannel.cpp works.
>
> can someone give me any pointers about this?
> to start with i'm happy with a proof of concept hack that sets 
> DTV_STREAM_ID to 1 on all dvb-t2 tuning attempts, then if it works i 
> can try and get a proper patch for it.
>
> i probably wont be able to get the mux editor or settings working 
> since i'm not familiar with how the setup gui works.
> but if i get a new optional mux setting for plp in place then i'm happy.
>
> _______________________________________________

I cannot directly help since I am not familiar with DVB tuning and I am 
in the USA where there is no DVB-T2. I think the best way to find out 
how it is working is to use a debugger to stop at some point in the 
code, examine backtraces and step through the code. You may want to set 
up a separate development system for that.

Changing setup is easy but it may require an extra database column if 
this is a new parameter for the channel. Is the PLP ID different for 
each channel? Is there a database column for it already?

Setup is different in MythTV version 29. Are you using V29?

If you do not have the time or the interest in debugging and figuring 
this out, please create a ticket so that somebody can look at it later. 
However it may be a long time before that happens.

If you do want to debug it and have questions about debugging let me 
know and I can try to help.

Peter