On Wed, 9 Feb 2005, M S wrote:
>
> Can you give me a newbie's guide to the differences between the
> Air2PC, pcHDTV HD-3000, and other HDTV solutions that work with myth?
> If I get two cards, would my machines (and AMD XP 3200+) be able to
> handle two cards? I can't put up an external antenna, so would I have
> to have a seperate antenna for each card? Can you have to HDTV cards?
> I'm a beginer at all of this, but I am pretty tech savvy and know
> some of the basics of HDTV, but very little about integrating it with
> Myth or any PVR for that matter.
>
My test system is also an AMD XP 3200+ platform and I've experimented with
the HD-3000 (along with an ATI Wonder Pro). I have an Air2PC coming my
way via UPS Ground from StormLogic right now. After I compare the two
I'll probably then order one more ATSC-class tuner before the broadcast
flag comes into effect and spoils the party. I've been experimenting on
the HD-3000 on my AMD XP 3200+ system using kernel 2.6.10-ac9. Here's
what I've learned so far:
CPU utilization for video capture is basically a non-issue. I think it
might be a few percent at worst. This is because there's no encoding
needed for capturing an ATSC broadcast since it's just an MPEG-TS stream.
CPU utilization for rendering HDTV is a whole 'nother matter.
Using mplayer and the x11 driver I can get 1080i to work with a Radeon
9200SE video card. But that isn't scaled video and since 1080i is also
1920 horizontal, you really need to scale the image down a bit.
Switching to the scaleable xv driver with this setup is a disaster. The
CPU completely saturates, the video stutters, and audio loses sync.
Switching to an nvidia FX5200 class video card (with the 1.0-6111 nvidia
driver) with this hardware helped immensely. I can run 1080i through
mplayer hardware scaled to a 1600x1200 screen and still have about 25% of
the CPU left. If I tell mplayer to use the ffmpeg codec library instead,
then I get about 30% CPU leftover.
Enter mythtv. Trying that same 1080i broadcast using mythtv coupled to
the pchdtv driver for live TV, I once again saturate the CPU and the video
stutters. I tried this using mythtv built from CVS from the time just
before the ffmpeg support was put into place so I imagine now things would
be better. I also had other major stability problems with this setup in
mythtv - one channel had no audio, and frequently mythtv would just hang.
Touching a non-existant channel in mythtv was the kiss of death for the
front end. After this experience I concluded that I needed a faster
processor and should wait for more stability in mythtv. Perhaps now
things are a lot better. I figure once 0.17 appears I'll try again.
I did some other experiments just using mplayer in order to prove in the
rest of the hardware and ensure that the pchdtv driver was stable. A 720p
broadcast could be rendered comfortably - about 40%-50% of the CPU left
over (again, this is mplayer not mythtv). A 480p broadcast was no sweat
at all. And just for grins I learned how to get mplayer to pass 5.1 audio
and got a nice 5.1 audio-encoded PBS broadcast working.
I expect that since the video *capture* part of the equation takes
virtually no CPU that having two pchdtv (or whatever) cards installed
should be no problem. You can do all this with one antenna; just use
normal signal splitters that you can pick up at your nearby electronics
store (or Target or KMart or whatever you live near). Every time you
split the signal, there will be a roughly 3dB loss in gain so if you have
to split it too many times you'll want to install an antenna amplifier
upstream. I found that cheap $13 antenna amps found at Best Buy work just
fine for this purpose. I'm using a TV antenna installed in my attic; I
think it's a fairly decent Radio Shack brand (oxymoron?) that's advertised
as "digital ready" - but it's just UHF spectrum (right?) so I don't see
why one would ever need a special TV antenna for this. This antenna is
currently driving the pcHDTV card, an ATI TV Wonder Pro, a Hauppauge
PVR-250, 4 NTSC TV sets, 2 VCRs and 2 stereo FM receivers. UHF signal
quality is nearly perfect across the board, and VHF channels 7, 9, and 11
are perfect as well. VHF channels 2 & 5 suck, but they always have around
here for me for the last 12 years (Chicago far west suburbs). Yeah,
there's a few antenna amplifiers scattered around in there too, including
a much more expensive Winegard device at the head end :-)
-Mike
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