mythtv and digital tv

[Jarod Wilson]

On Fri, 2008-07-25 at 07:11 -0400, Frank DiPrete wrote:
> 
> Ben Scott wrote:
> > On Thu, Jul 24, 2008 at 6:36 PM, Frank DiPrete <fdiprete at comcast.net> wrote:
> >> I like the HDHomeRun card ...
> > 
> >   Just to make sure it's clear, the HDHomeRun isn't a card, it's an
> > external box (about the size of a cigar box).  It uses a wall-wart
> > type power supply transformer.
> > 
> >> If the card had hardware encoding it would be perfect.
> > 
> >   Encoding or decoding?
> 
> Encoding on the backend where the card goes.
> 
> http://www.pchdtv.com/hd_5500.html
> 
> The HD-5500 Hi Definition Television PCI Card is an universal PCI 2.2 
> compliant card. The card receives NTSC, ATSC and Cable/QAM Signals and 
> converts them to digital streams which are transported across the PCI 
> bus. Display and MPEG2 decoding are done on the host computer
> 
> > 
> >   For digital broadcast -- be it cable or ATSC OTA -- the stream is
> > already encoded and compressed as part of the transmission process.
> > There's no need for an encoder.
> > 
> 
> The description isn't clear about writing the streams to disk.
> 
> The goal is to write mpeg2 files to the server for playback like the 
> pvr-250 does via its encoder. I'd like to believe that the term "digital 
> streams" means mpg2/aac but the term "digital streams" isn't defined on 
> the site. I'll check some mythtv sites about this card to see what is 
> involved.

"Digital streams" definitely means mpeg2 here. HDTV (and all digital
video) over the air and on cable in the US is always mpeg2, encoded as
such as the head end. Digital tuner cards more or less simply tune into
a broadcast mpeg2 transport stream and dump it to disk.

> >   For decoding, I believe you'd still be able to use the "small quiet
> > diskless box frontend".  The one thing I'm not sure about is: I expect
> > not all hardware decoders are created equal.  It may be the decoder in
> > your front-end box can't handle this new-fangeled high-def stuff.
> > 
> 
> The only prediction I have here is "probably OK". playback of the 
> recordings I make today (ntsc analog to mpg2/aac at 48K sampling - file 
> is a bout 2G per hour) takes 25% of the via cpu while using the mpeg 
> decoder chip.

Depends heavily on the generation of your video controller... Many of
the unichrome video chipset mpeg2 decoders can't handle larger than
720x480 streams. I forget which one is which anymore, but the first-gen
one on an EPIA M10000 board definitely doesn't cut it (I have one). I
believe unichrome pro II definitely *should* be able to, others, not
sure..


-- 
Jarod Wilson
jarod at wilsonet.com