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

[matt.jarvis at philips.com]

Dear Richard

I'm very interested in getting this to work, so lets' keep this thread 
going and encourage some discussion about the problems that would be 
associated. 

Your idea for a complete rewrite of Myth seems a bit drastic - and I'm not 
sure the main developers on this project would be overly keen on a 
fundamental change like this ( perhaps Isaac would like to comment ) . I 
understand your principle in abstracting the actual video source, so the 
interface with myth is generic and a whole range of plugins could then be 
used , but perhaps in the short term it may be possible to get this 
working the short and dirty way via piping and vloopback - as a proof of 
concept before changing the myth interface in this way.

I completely agree the decoding to re-encode is wasteful, but considering 
that in order to run myth most people are using way powerful processors 
anyway, there certainly looks like there should be enough cpu cycles 
floating around to not make this an issue ( my box has an athlon xp 1800, 
with 512mb of memory. )

With reference to ts2ps I see your point - that this would actually have 
to be invoked by the channel change script rather than at an earlier 
point, unless perhaps it is possible to demultiplex all the streams simultaneously. Again this is mostly conjecture on my point 
as I haven't played with any of this code yet, just done a lot of reading 
around the docs to see if it would theoretically be possible to integrate 
dvb-t into myth.

Vloopback should be easy to test out, if you have read the docs correctly. 
I am still a little confused as to the docs :

For example: if you have a camera on /dev/video0 the input pipe will most 
likely
be /dev/video1 and the output on /dev/video2.
e.g. if you want to watch an inverted image of the camera you would start 
invert
with /dev/video0 as its input and /dev/video1 as its output.

This seems to suggest that you still need a v4l device as an input !!


Matt

Matt Jarvis
Product Marketing Manager
Marantz Professional Europe
Kingsbridge House, Padbury Oaks, 575-583 Bath Road, Longford, Middx, UB7 
0EH, United Kingdom
+447796610410 - Mobile
+441753686080 - UK Office
+441753686020 - Fax
matt.jarvis at philips.com










Richard King <rak at cs.man.ac.uk>
2003-03-18 18:54

 
        To:     mythtv-dev at snowman.net
        cc:     Matt Jarvis/LGD/CE/PHILIPS at EMEA1
        Subject:        Re: Adding DVB-T support to MythTV
        Classification: 



Hi Matt,

> Yep, I think MJPeg tools would definitely do the conversion to various
> different video formats, while ts2ps would demultiplex the initial
> transport stream.
It will. though as as I said in my last message you're going to have to 
have a way of telling ts2ps which PID's you want. 

> The only problem then is to get this stream into a
> virtual v4l interface ( if indeed this is possible ). I did look around
I'm not sure this is the most useful way of doing it. Myth currently 
doesnt support incoming MPEG2 streams from a V4L device and I'm not sure 
the V4L api supports datastreams with both the audio and video embedded. 
It would certainly take a while to implement this in Myth so you might as 
well write some direct support into Myth.

If you meant decoding the MPEG2 stream and then feeding it into the V4L 
subsystem this is definately possible with something like vloopback 
(though it might need a bit of work to get it into a useful shape for 
this - disclaimer: only looked at it for 2 mins :S ) This method is going 
to be incredibly wasteful of resources though.

> on the web to try and find out if it's possible to pipe a stream in this 

> way but couldn't find anything referring to similar stuff - if anyone 
> knows how to do this I will certainly test it out. I would also imagine 
> there would be timing and synchronising issues. 
vloopback looks like a good start. You said in another mail that it only 
supports sending from a V4L device, my initial impressions suggest this is 

not the case, though they are VERY initial impressions ;) AFAICS vlookback 

requires you to feed a virtual V4L device (say /dev/video0) and it will 
then mirror than input out on another V4L device (say /dev/video1). As 
long as you have a program that can feed it the video in the right format 
it should work

> 
> As I said in my previous mail the channel changing would require a 
> script and a config file. The config file lists the channel frequencies 
> on the dvb signal, and cross references them to the mythtv epg. This 
> would need to be filled somehow by tv_grab_uk, or perhaps generated 
> automatically by another script. The channel change script would then 
> convert the mythtv channels to the correct frequency and call dvbtune. 
In some countries it should be possible to get the data for the EPG out of 

the transport stream. (I think freeview in the UK only broadcasts Now and 
Next information right now though)

> 
> However, even on the initial feedback to this post it certainly looks 
> like there is some interest so here's hoping someone picks this up and 
> runs with it. I'm available for testing, documentation and other 
> non-programmer type stuff ..... 
This is my /big/ project when I finish uni this summer, assuming I'm not
beaten to it. My intention is to make Myth support a form of plugins to
support various inputs with my target being: V4L, DVB and internet
streams; with FM radio, DAB and American Digital TV/HDTV being easily
supported if someone wanted to write the support.

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




-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/attachments/20030319/3903d2ff/attachment.htm