[mythtv-users] XvMC on NVidia with Myth .20 (Anyonegetting goodHD off a P4 3

R. G. Newbury newbury at mandamus.org
Mon Jan 8 19:23:33 UTC 2007

Drew Bernat wrote:
> On Jan 8, 2007, at 11:51 AM, R. G. Newbury wrote:
>> You appear to have missed the point here, and it is amazingly easy to
>> get confused about what is being discused.
>> There are two types of signal delivery.
>> There are (for our purposes) two levels of signal definition.
>> One type of delivery can do both levels of definition.
>> The other type of delivery can do only the lower level of definition.
>> Digital delivery can be SD or HD level definition.
>> Analog delivery can only do SD delivery.
> Right. So my HDTV cards can record HD- or SD-, and the PVR-500 record 
> SD-. I'm outputting SD. Right so far?

Right. Your "HDTV" cards will only do 'HD' if they are fed an HD 
definition signal. Generally, that means OTA with an antenna or you are 
in the US, where you can get unencrypted HD over cable for local (OTA 
avilable) channels. If you are getting encrypted HD, then the output 
form the STB is either by firewire or S-video, and in either case, will 
not use your HD card to tune the signal.

>> These *should* be the same, but realistically the digital will be a
>> better picture. The one is sent as MPEG and streamed to your hard drive.
>> The other is sent as analog, and converted by your PVR's onboard
>> encoder, and streamed to your harddrive.
> The HD-card-recorded programs are definitely clearer. What I'm wondering 
> is if the HD-card-recorded shows work with XvMC, and the 
> PVR-card-recorded shows don't - it might be a format difference between 
> the cards rather than a resolution issue.

Whoa... XVMC is explicitly a video card driver thingy. It has NOTHING to 
do with the tuners. XVMC makes use of the video card *hardware* to do 
stuff which would otherwise be done by the main CPU is producing the 
video output. Which is why you see discussions of the computer power 
needed to decode HD. You need either a pile of computer grunt, OR an 
Nvidia or VIa video chipset which supports XVMC.


>>> Also interesting that the S-video out ignores modelines. I know you can
>>> futz with resolutions, but I thought you could also do refresh rates. I
>>> guess not.
>> Well, technically, I guess it has a hard wired modeline based on NTSC or
>> PAL standards... which include the refresh rate.
> Okay, so I can safely ignore the discussions on setting modelines and X 
> overhead.
>> Clean down your xorg.conf to either 800x600 or 720x480 and see what
>> happems. Since you are using the S-video for output, remember to set the
>> output to 'CRT,TV' to get both.
> Will do, thanks!
> Drew
> -- 
> Drew Bernat
> abernat at zathras.net
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