[mythtv-users] Re: HDTV, Myth, HD-2000, HD-3000, questions galore (and hopefully answers from the smart people... )

[Paul Leppert]

Blammo,

How about questions related to HDTV setup in mythtv?

- How are HDTV channels set up? Using zap2it and an HDTV lineup
resulted in a mix of NTSC and ATSC channels with incorrect freqid for
the digital channels (e.g., in Chicago, Channel 7 (ABC) is actually
broadcasting on 52).  How is this set up via mythtv?

- How are HDTV subchannels set up?  Again, based on above, ABC is
multicasting on 52.  In mythtv, are the channels specified as freqid
52-1, 52-2?  or some other format?  How should these multi-channels be
set up for names (mythtv channel input won't allow '.' (7.1, 7.2,
etc.) or '-' (7-1, 7-2).  Do these channels need to be renumbered
(e.g., 900, 901)?  For me, I cannot seem to get any other subchannel
other than the first regardless of what I put in the freqid field in
mythweb (using an HD-3000).
- Based on http://thegeorges.us/mythtv instructions, the mythconverg
database needs to be tweaked to set channel format to ATSC (assuming a
default of NTSC).  Is this necessary?  What are the correct commands
for setting this up?
- If your mythtv setup receives OTA NTSC and ATSC, is there any reason
to keep the NTSC channels within mythtv?  If so, how should these be
set up (similar issues as above since you now have two (or more)
channel 7's)?  Is there a priority scheme within mythtv to make sure
it records a show off the ATSC stream before choosing the same show on
the NTSC stream?
- Does transcoding need to be set up in mythtv for HD channels (my
understanding of the HD stream is that it contains all subchannels. 
Does mythtv filter out the "extra" subchannels or do you need to use
the transcoding mechanism to reduce the file sizes?)  I have no idea
how any of this works in mythtv.

And questions for performance:

- What components of the mythtv / computer setup impact performance of
HDTV (e.g., at a given hardware level, what is the CPU usage for
recording?  what is it for playback, what is it for both)?
- Related to above, what is the impact of multiple HDTV captures
(e.g., two HD-3000 cards) on the processing requirements of the PC? 
Anybody here yet?  Anybody have an idea of what it takes
processing-wise for HDTV PIP with two cards?
- What can be done to improve performance (how is resolution reduced? 
Is there any impact (or even capability) of recording at lower
resolution than 720p or 1080i/p? Is there an easy way to playback at
different resolutions (via mythtv rather than different modelines).
- If a modeline is set up for a particular monitor at a particular
resolution, does that automatically reduce the processing of an HDTV
stream (in other words, if I'm playing a 720p ATSC stream (1280x720)
back on a monitor at 480p (704x480), have I somehow reduced the
processing impact, or is the mythtv box still handling the full
processing impact and all that is happening is a reduction in quality
on the output)?
- For playback, what is the processing impact for different
resolutions (playing back a 720p stream at 1280 x 720, 1024 x 576, 800
x 450)?
- For those trying to get the best performance (at the tradeoff of
quality), what is the best way to play back HDTV?  Reducing playback
resolution?  Transcoding to reduced resolution? etc. etc.
- What about audio?  Are there general rules about digital audio and
performance or is this generally "not an issue" based on using a 5.1
sound card (e.g., SB Audigy)?
- What is XvMC and how does / will that help with the processing
requirements of HDTV playback?  Are there particular video cards this
will / will not work with?  Anyone have real world examples of
processing improvements (e.g., CPU usage) with XvMC and without?

And a general question:

- Is there a way to tell within mythtv what format the ATSC is being
broadcast (720p, 1081i, etc.)?


Wish I had more answers than questions, but as I get up the learning
curve (and I receive my new, faster CPU), I should be able to
contribute some real-world experience with my HD-3000 (and PVR-250 if
I can ever get them working together).

Thanks,
Paul
-- 
I hear and I forget. I see and I remember. I do and I understand.  --  Confucius