[mythtv] Re: Adding DVB-T support to MythTV

Richard King rak at cs.man.ac.uk
Tue Mar 18 18:30:39 EST 2003


Appologises if my mails screw up threaded mail readers, I'm replying by 
pasting stuff from the web archives because I wasnt receiving mailing list 
emails.

Hi Edward,
  
> > 2) The budget cards don't tend to do any demultiplexing (the Hauppauge
> > doesn't) so you will have to integrate a MPEG-TS demultiplexor at the
> > recording stage. This needs to be able to determine which of the
> > element streams contain the video and audio streams for the channel
> > you want to watch. This will need database modifications in myth. 
> 
> I would have assumed that the cards have the concept of a "tuner" and so 
> you get just a single meg stream out of them. demux should be a fairly 
> straightforward case of running a demux filter on the mpeg stream? 
>
> I wonder if there are complications with multiple audio streams though?
> Does this happen? Stereo + Mono + directors comments, etc..?

They do indeed have the concept of tuner and you do get a single mpeg 
transport stream out of them. However this stream contains upto 8 video 
channels, multiple audio channels per video channel or on their own for 
DVB radio, VBI data channels, MHEG channels (i think thats right - 
interactive tv stuff) among others. So the challenge is to only extract 
the channels you need rather than saving the entire 20+mbit/s stream. The 
hackish way of doing is to parse an existing channel.conf for the list of 
streams the non hackish way is to adapt the way Myth stores its channel 
information to include the necessary details.

> > 
> > 4) You will either have to write code to put the MPEG element streams 
> > into the NUV files or add support for native MPEG files in MythTV. 
> > Possible issues with Timesyncing and seeking. 
> 
> Is this hard...? I will have to have a look at the NUV website to find 
> out more. If NUV files can't package an MPEG stream then I think this 
> presents a significant barrier... 
It shouldnt be too hard. I'm really not sure about this but I believe the 
NUV files store each frame with a header. Therefore the reason i mentioned 
this was that you would have to parse the incoming MPEG element stream and 
seperate the frames for storage in the NUV wrapper. I may well be wrong 
and if I am then its very easy.

> 
> > 5) You will have to add MPEG-2 video decoding and possibly MPEG-2
> > Audio or AC3 decoding to the playback side of Myth. This is all
> > supported in libavcodec (i think) so shouldn't be too hard.
> 
> It might be very useful as well. I am guessing that lots of good ideas
> are in mythvideo for how to handle this?
I don't think so. MythVideo just calls MPlayer AFAIK. It can't deal with 
the live streams. 

-- 
Richard King
E-mail: rak at cs.man.ac.uk



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