[mythtv] pcHDTV NTSC<->ATSC

Wed Sep 15 13:43:10 EDT 2004

On Tue, Sep 14, 2004 at 06:16:14PM -0500, Jason Hoos wrote:
> I recently looked into getting both ATSC and NTSC working on a single pcHDTV
> card, mostly because I had defined two sources on my card (one off each
> antenna), one source being HDTV and one source being cable.  When I did
> that, Myth kept locking up anytime I switched to an NTSC channel.
> 
> Off the top of my head, here is what I discovered.  Fixing the problem for a
> record-only setup shouldn't be too bad - in tv_rec.cpp, you need to modify
> the function that sets up the appropriate Recorder class so that it checks
> whether the channel is ATSC or NTSC, and have it instantiate an HDTVRecorder
> or NuppelVideoRecorder as appropriate.  In addition, some changes to the
> Channel class were necessary in order to keep it from trying to check signal
> strength on an NTSC channel.  

Basically the same changes I was about 90% done on incorporating.

> 
> Those were the changes I made so far, and they seem to be steps in the right
> direction, although I didn't test recording really since my initial goal was
> to get things working in Live TV, since that was where the lockup was
> occurring.  Getting things working in LiveTV, however, is more difficult,
> and I got sidetracked before I made any major headway with it.  
> 
> The main problem with Live TV is that when you enter Live TV mode on the
> pcHDTV, Myth pretty much sets up everything it needs up front in order to do
> ATSC, and there isn't really much provision (that I could see anyways) for
> switching to NTSC on a per-channel basis.  When LiveTV starts up, the
> backend creates the HDTVRecorder object and the frontend creates a
> corresponding AVFormatDecoder object, and they persist until you exit Live
> TV.  The class in tv_rec.cpp doesn't really have any facility currently for
> switching back and forth between using HDTVRecorder and NuppelVideoRecorder
> when changing channels, and I'm guessing that a similar situation exists
> with the decoders in the frontend, although I didn't get that far.

So... what does it do currently if you have a pcHDTV and say a Hauppauge card as seperate backends... When you change between channels served by different cards it changes both the frontend and backend to vary the record and playback objects. I have not looked to deeply but I am thinking that putting an extra check in to see if (even if we stayed on the same input source) the channel type has changed. If so fire off the same exact processes as if it were a different input that we were switching to.

I need to look more into this... if one record and playback option is instantiated for each input when WatchingLiveTV is started then that idea is screwed. However even in that situation should be able to just make 2 objects for the card instead of 1... As long as the CheckSignal is smart enough to know channel formats we are then safe. I think :}

> 
> I toyed around (mentally) with various ideas to either get tv_rec to be able
> to switch recorders, but I haven't come up with anything yet that seemed
> elegant.  Once that gets solved, there's still the issue of whether the
> frontend needs logic to switch decoders (unless somehow it already can), and
> whether or how the backend would tell the frontend that it needed to, etc...
> 
> If you want, I can share the changes I made so far if I still have them (not
> sure if I do or not), since they may work sufficiently at least for
> scheduled recording.

I would love to compare them to mine..  nothing like 2 programmers hitting one subject to find an eligant solution. :}

> 
> Jason
> 
> 
> mythtv-dev-bounces at mythtv.org <> wrote:
> > I don't believe anyone is working on this. Doug, John Poet and me have
> > been doing work lately on HDTV. Just to warn you, you'll need
> > to fiddle
> > a few things to get this working.
> > 
> > -- Daniel
> > 
> > On Mon, 13 Sep 2004, Todd Freeman wrote:
> > 
> > ]Howdy all...
> > ]
> > ]I have been salivating over what my pcHDTV card can do in
> > ATSC mode...
> > ]and now have gotten it in my head to go ahead and see if I can get
> > ]Mythtv to use it in both NTSC and ATSC mode...
> > ]
> > ]Before I go doing massive code writing I wanted to check and see who
> > ]the programmers were that are working on the core pcHDTV stuff for
> > ]Mythtv. ]
> > ]Basically I don't want to step on anyones toes or to dupe effort
> > that ]is already being worked on. ]
> > ]So far I have noticed that with the card set as a pcHDTV card you are
> > ]locked into ATSC no matter what the channel table says the channel
> > ]really is. I have thought of a couple fairly easy ways out of
> > this... ] ]Also perculating in my head is the idea to have mythtv
> > change it's ]capture type and also switch the pchdtv over on channel
> > change. ] ]Anyways... any info would be great
> > ]
> > ]Keep up the good work everyone!
> > ]
> > ]
> 
> 

> _______________________________________________
> mythtv-dev mailing list
> mythtv-dev at mythtv.org
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-dev

-- 
Todd Freeman  Ext 6103                   .^.    Don't fear the penguins!
Programming Department                   /V\
Andrews University                      // \\    http://www.linux.org/
http://www.andrews.edu/~freeman/       /(   )\   http://www.debian.org/
                                        ^^ ^^
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
Url : http://mythtv.org/pipermail/mythtv-dev/attachments/20040915/529ab1c5/attachment.pgp