[mythtv] vps once again...

maestro waggawagga at gmx.net
Wed Jul 28 16:17:17 EDT 2004

> I had a quick look at this code, but I could not see any decoding of the VPS. 
> But it does show how to aquire various VBI data.

well i used the word decode as it appears in the function name
"decode_vps" and since binary vbi information is displayed as human
readable datetime information. (as i allready said im not an english
native speaker)

> This buffer is coming from the AvFormatDecoder, which handles the MPEG2 
> decoding. This buffer is defined in EN 301 775 (Vbi data in dvb) and contains 
> many vbi data lines. What this function does is to demux it, and feed the 
> teletext line data to the teletext decoding function. There are also stubs to 
> mux vps/wss/cc and so on to other decoder functions, but I have not seen 
> these data types yet, hence no point for me to decode them.
does this mean, that your teletext function only works for vbi data that
comes with dvb signals and thus does not work for cards like pvr's and
bttv based cards? i assume its working with them aswell, but to know for
sure is always better.

> What I would do, is to add a function similar to the processPesPktData to 
> demux the data from the ivtv vbi device. It would look something like the 
> process function of the example vbi.c. Then you would make a VPS 
> decoding/parser function similar to the ::line function that would be general 
> enough to suit data from both ivtv and dvb.

so do you suggest that i insert my code into your codebase and create my
own patchset (based on mythtv cvs, and your patchset)?
> Right now, this VbiDecoder is only suited to be placed on the frontend. Since 
> the VPS really is backend related, I would like to see this beeing 
> implemented outside it, or better, that the decoder would be told if it lives 
> on the backend or frontend. I also want to make an extension to it so that 
> teletext data can be muxed out of a recording and be transmitted as an extra 
> stream, and that only recording related stuff such as subtitles/wss/cc is 
> ever stored in a recording.
> I would say that VPS info should be sent to the Scheduler, so that it can try 
> to match it's own recording list to the info that VPS sends. With a general 
> interface to feed data to the Scheduler and decoding of the line data in 
> VbiDecoder, this should be very easy to expand to other data types.
if i get this right, it would make me append some function to the
scheduler that accepts (retreives) vps-data that matches a current show.
(e.g. the scheduler collects vps information when it is supposed to
start a new recording)
> I find these documents valuable (all can be downloaded www.etsi.org):
> EN 300 472 - Teletext in DVB
> EN 301 775 - VBI Data in DVB
> EN 300 231 - Video Programming System
> EN 300 294 - Wide Screen Signalling
thanks i'll take a look at them. 
> Hope this helps.
me aswell

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