[mythtv-users] HD on SDTV playback question

[Steven Adeff]

On 2/25/07, Gary Raposo <gary at raposo.ca> wrote:
> At 03:26 PM 25/02/2007, you wrote:
> >On Sunday 25 February 2007 12:26, Steven Adeff wrote:
> > > On 2/25/07, Paul Bender <pebender at san.rr.com> wrote:
> > > >
> > > > Most of the frontend's power is used to decode the video. Therefore, the
> > > > power needed depends on the resolution of the content much more than the
> > > > resolution of the display. Of course, by today's standards, a below
> > > > average computer system can decode and display HDTV.
> > >
> > > If the other frontends have an FX5200 or better you can use XvMC to do
> > > the decoding if the CPU isn't fast enough.
> >
> >Up to a point, yes, but XvMC isn't a magic bullet. On my system (an Intel
> >Celeron D 3.06GHz), using XvMC with an nVidia MX4000 and nVidia's drivers
> >produces smooth playback with CPU loads of around 50-60% for mythfrontend
> >when playing back HD content on an SD screen (800x600 resolution), with X
> >chewing up another 5-10%. Disabling XvMC but using the same card kicks CPU
> >use up to around 80%, IIRC, with playback remaining smooth -- but it gets
> >unsmooth quickly whenever you do anything (skip back, etc.). Swapping in a
> >video card based on a SiS Xabre chipset, which can't do XvMC, produces choppy
> >playback with higher CPU loads for both mythfrontend and X (around 80% for
> >mythfrontend and 20% for X, IIRC). Cutting playback speed down to 60-90% of
> >normal typically produces smoother playback. Based on this, I'd guesstimate
> >that XvMC reduces HD playback CPU load by 25-50%. This is good, of course,
> >but it's nowhere near as much of a reduction as you see when using hardware
> >encoding cards vs. simple frame grabbers.
> >
> >That said, results are likely to vary from one card to another. My
> >understanding is that the cards with the most hardware acceleration delivered
> >by XvMC are those based on the nVidia 5200FX series.
> >
>
> Sorry to butt into your discussion but you've touched on something
> that I've been wondering about for some time now.  I've got an
> original Asus Pundit (2.4GHz P4 with onboard SiS chipset driving its
> S-Video TV-out) configured as a SD frontend.  My backend is capturing
> HD (it's also my primary frontend driving an HD display).  I haven't
> had any success with smooth playback of HD content scaled down to SD
> on the Pundit and I assumed that the processor was simply not up to the task.
>
> Are you saying that if I go out and get myself a 5200FX based video
> card and turn on XvMC then I'm in business?  Remember that this video
> card would have to be a PCI based card... not AGP or that newfangled
> PCI-E.  Do you think this configuration could do it?

Gary,

I believe it was determined that with XvMC enabled the PCI bus is
capable of handling 1080i display. It would probably behoove you to
search the list archives first to be sure, but I believe that was the
conclusion that was made. The other option, if possible, is to upgrade
the processor on the Pundit to something that can handle 1080i
decoding.

-- 
Steve
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