[mythtv] DVB development

[Kenneth Aafløy]

On Tuesday 25 May 2004 07:12, Martin Bonner wrote:
> I've been using myth for a while with analogue capture cards but have
> recently put together a box with a DVB-T nova card.
>
> Searching through the list archives, I've come across a number of
> discussions relating to DVB development, but little to indicate what is
> currently being worked on or what the state of play is at this point in
> time.
>
> Specifically, I was interested to know whether these is any work underway
> on the following features:-
>
> 1) Recording multiple channels on a single card (from a single multiplex)
> As far as I can see, this is going to require some pretty substatial
> changes to the database schema for the whole cards/sources/channels setup,
> which in turn is likely to require a fair amount of changes to existing
> code that relies on the current schema.. have any decisions been made yet
> as to what the new schema needs to include, or as anyone working on this at
> the moment? I'd be happy to try and work out a schema for this if it has
> not already progressed beyond that point.

I wrote a perliminary kind of hackish patch for this a while back, but it was 
scrapped most of my channels are encrypted and my conax cam rejects to 
decrypt multiple channels at once. The patch did work for uncrypted channels, 
and I sent it to the dev list in the hope that anyone with some interrest 
would continue to work on it, but nothing significant happened.

Your approach would be something like this:
	- Make all DVB classes aware of the difference between primary (the first 	
		opened instance of a card) and the following instances.
	- Make a clean method of specifying the fact that not all configurations can 
		record multiple channels (we need some sort of cam setup eventually, and 
		this config could include a flag whether the cam can do this kind of work).
	- Make the TVRec class aware of 

> 2) Recording audio only channels (without using the 'use the video pid of
> another channel on the same multiplex' workaround)
> There seem to be two main issues to address here, firstly support for audio
> only recording by the backed, and secondly, some way for the frontend to
> know whether it is supposed to be waiting for video frames, or just playing
> audio. I wondered whether this might be worth looking at in conjuction with
> other 'no video stream' cases such as trying to view an encrypted channel
> without the relevant cam and/or subscription, or channels which are not
> transmitted 24/7?

Are you really unable to record a radio channel without using a video pid? Are 
you sure that you are not only talking about playback of audio only as a 
problem?

Another issue in the same context is the support for multiple languages and/or 
audio types. I have a simple method of supporting multiple audio streams in 
my tree, by selecting the first stream available. This is done, so that I can 
at least record multiple audiochannels. I was hoping to extend this to be 
able to describe the streams in the interface of AVFormatDecoder, and make it 
able to switch audio streams midplayback.

> 3) Subtitles (Closed Caption)
> Is anyone is currently looking at DVB subtitle support? if not, i'll start
> taking a proper look at this and see if I can get anywhere with this. The
> main issues with this seem to be the additional complexity of DVB
> subtitling data compared with anologue, in particular, the support for
> bitmaps and for specific placement of subtitle data.

I belive nobody is working on it. From what I've read about subtitles, they 
are just a monochrome bitmap of sorts. There is also awailable regular 
teletext data on some channels, which it would be nice to have piped to the 
vbi decoder in mythtv. The subtitle format of dvb is the same as is carried 
in a dvd format stream, and is described in 

BTW: Wrote this reply a while ago, but only recently got to look over my 
drafts folder. If it contains strange statments, blame and yell at me, ok?

-- 
Kenneth