[mythtv-users] Standard PCI VDPAU-capable Video Cards vs. PCIExpress

Brad Templeton brad+myth at templetons.com
Sun Nov 28 22:32:00 UTC 2010


On 11/28/2010 11:52 AM, Robert Longbottom wrote:
>
> On 28 Nov 2010, at 06:07 PM, Brian Wood<beww at beww.org>  wrote:
>
>> On Sunday, November 28, 2010 10:57:50 am Robert Longbottom wrote:
>>
>>>> How about the OSDs? Are they OK?
>>> Yes, the osds were fine - I assume you mean during playback?
>>> Everything just worked.
>>>
>>>> May I ask what mobo you are using? Most of them have a BIOS setting
>>>> to tell it what graphics card to use first, this might correct the
>>>> booting problem.
>>> No idea. It's a small form factor HP business pc that I got from work
>>> when they were selling them off for £30 as part of an upgrade.
>>>
>>> I did have a fiddle around with the various settings in the bios but
>>> never managed to find a combination that worked. I think I ended up
>>> wit the on board graphics disabled, an old-ish nvidia agp card and
>>> the Sparkle pci card in it. That's the only way it would boot!  The
>>> bios and text console display on the agp card and I configured X to
>>> run on the pci card.
>>>
>>> Sadly the agp card wasn't new enough to do vdpau and I couldn't find
>>> a low profile agp card that would. Thankfully the pci slots were
>>> turned on their side it would take a full height card.
>> I'm not aware of any AGP card that will do VDPAU. If I could find one I'd
>> jump on it immediately. The only ones I have found are either PCIExpress
>> or PCI.
>>
>> If I've missed one I'd love to hear about it :-)
> I don't think so. I'm fairly sure I looked for any vdpau capable agp card about a year ago and drew a blank.  It was hard enough at the time to find a fanless pci card that I could get in the UK.
>
> Robert.
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This works -- I have a PCI 8400GS card in my old Pentium-4 frontend, but 
there are some important caveats.   It's a tradeoff, because the P4 is 
able to decode mpeg-2 1080i in software, but not able to handle 1080 
line mpeg 4 movies as you might download.   The VDPAU is able to play 
both types of video.

But you will *only* be able to play HD video in the 4 VDPAU supported 
formats.  Other videos, including the ones you made with mythtv's 
transcode, will not play properly in software players, because the PCI 
bus doesn't have enough bandwidth to shove 30 frames of 1920x1080x4 
bytes every second into the card!   In fact, I believe it does not have 
enough bandwidth to even do 720p.     PCI just isn't a very fast bus.  
VDPAU works because you are sending partially compressed data into the card.

I've wondered if I might be able to hack it to bring up the on-board 
video in the box and see if that can play software decoded HD, but that 
would mean having to switch inputs on the TV while playing it.  Messy.

I also found that in spite of speed reports, if you want to do things 
like audio speed up and nice OSD, you can't use the fancy deinterlacers 
in vdpau.   You can use the more basic ones at 2x mode, so they still 
look pretty good, but if you try to use the advanced ones, you will find 
that any appearance of the the OSD  makes the video skip a bunch.

(Right now, audio speed up isn't working at all in the TRUNK version I 
compiled last week.  It seg faults, and I don't know if VDPAU is to 
blame as it doesn't do it on a different frontend compiled from the same 
code.)

On the whole, I was not that happy with my decision to go to PCI 8400gs 
with vdpau.  The regular operation of Mythtv (playing mpeg2s) is only 
modestly improved.  Losing the ability to play other formats including 
my old transcodes was annoying, though the ability to play downloaded 
mp4s at HD was good.   So I stayed with it, but I guess it's not 
something I would go nuts to do.

If you can, the obviously answer is a new motherboard, since you can now 
get a dual core chip and motherboard for peanuts with PCI-express.   The 
only reason I didn't go that way is my frontend is an Aopen cube SFF 
computer, and you can't get new motherboards for this particular one as 
far as I know.   That's why I won't be buying any more SFFs with custom 
sized motherboards.  They are cute but they limit you.


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