[mythtv-users] HDTV - PVR: Does it work?

Brandon Beattie bbeattie-maillist at linkexplorer.com
Tue Jan 20 23:37:13 EST 2004

On Tue, Jan 20, 2004 at 03:51:05PM -0800, Ian Neubert wrote:
> Andrew Dodd [atd7 at cornell.edu] wrote:
> >You'll need a better video card and possibly a faster Athlon to think about
> >using the pcHDTV...  Software decoding of HDTV (even with motion
> compensation
> >and IDCT acceleration by the vid card) pushes modern CPUs to their limits.
> Yikes. Lol. I do have another box that I could use for a frontend, a P4 3
> GHz w/1 gig of ram and an ATI 9800XT. Am I right in thinking that my
> lower-ish(!) end Althon 2400+ could handle the stream captures of the
> pcHDTV? Then the question is can a 100 meg switched network handle streaming
> of an HDTV stream and also will my faster box be able to decode it?

Easily.  I was going to rig a p3 450 to do all my backend work but there
was an incompatibility with that motherboard pci version and the card.
(It was a very old p3 system).  Saving a stream requires little/nothing.
The 2400 would be perfect though if you plan on transcoding the mpeg2 to
mpeg4 and removing commercials.  It will take about 1.5x as long to
transcode, depending on what quality you set transcoding to (Which is
still in the works).  I think the amd system is just fine for a backend
system, and that is what mine does now.

1080i is the highest bandwidth HDTV stream at 19.6Mb/s.  A full ATSC
stream can be up to 45Mb/s but this is only if you save all the
subchannels(Which would have to be maxed out)  Most atsc streams are
14-25Mb/s that I see on my 11 HD stations.  The HDTV streams come
through as transport streams (MPEG2-TS) which contain redundant
information for i frames in the mpeg codec just incase some data is lost
in transmission.  Douglas and others have already taken a few steps to
remove this and turn the mpeg2-ts into mpeg2-ps (No redundant data such
as used for DVD's).  This cuts off some useless bandwidth once the
stream is received.  (About 10-20% with little CPU usage).  So the end
answer is you shouldn't push more than about 20-25Mb/s from the backend
to the frontend for watching a HD show.  a 100Mb/s connection is plenty.

Expect about 70% load on the p4 3.0Ghz to start with.  Turn on the
extras (commercial detection, denoise, de-interlacing) and it will go to
mid 80's.

> >I also made the mistake of buying an MDP-100...  DIE TERALOGIC DIE!!!
> Seriously, I don't get why this thing is so freakin expensive either. To its
> credit though the MDP-120 has a good HDTV tuner, I was able to get perfect
> picture & sound when it claimed 30% signal strength.

I wonder if 30% is really 30%...  So you know, it takes about 70% for a
good signal on the pcHDTV.  I'm 15 miles from most towers and run
through 150 feet of rg6, a 3-1 splitter and still get 92-95 signal
(Never using any amplifier... And it was a $20.00 radio shack Yagi UHF
antenna (Mounted outside is the key)


> >Too bad the developer of the TL880 Linux driver had to go on vacation or
> >something.  TL880 driver development has been halted until late 2005 or
> when
> >someone else takes over the driver.  :(
> >Theoretically IF the TL880 driver were finished (at least to the point of
> being
> >able to record the transport stream), it could be used just like the pcHDTV
> to
> >perform recordings and then display in software.  Or you could use the
> pcHDTV to
> >capture and the TL880 to display on a lower-end machine.
> I'm going to return this hunk of junk tomorrow, and just eat the $60
> restock-fee. :( But at least I still can. I hope someone takes up that
> project and gets some usable drivers for you!
> ..................
> ..................
> ............ian...
> ..................
> www.ianneubert.com
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