HD with Xvideo on i915GM (i810 driver)

Andrew J. Barr andrew.james.barr at gmail.com
Sun Nov 5 12:00:30 PST 2006

On Sunday 05 November 2006 13:42, galenz at zinkconsulting.com wrote:
> 1) For proper HD performance, you will have to compile and install
> the drivers yourself. Most if not all distributions (even the new and
> shiny FC6) do not ship versions that are up to date. Plan on hitting
> their git repository to do this. You may also need to increase the
> LinearAlloc value in your xorg.conf file for 1920x1080 (technically,
> 1920x1088) resolution HD video to properly play.
> 2) This card supports XVideo acceleration, not XvMC. Please correct
> me if I'm wrong, but this means we're offloading scaling, color
> conversion, etc. but nothing else. This is not the maximum amount of
> acceleration possible, but as far as I know, Intel has not released
> documentation on the GMA 900/950 for better acceleration. The chip is
> capable of it and the previous generation Intel chips even supported it.

Yes, but they support very little actual hardware-based decoding from what I 
can tell. The GMA 9xx series up to the 965 are similar, I think that while 
the 900 and 950 chips supported some more hardware decoding than then 8xx 
chips, the 965 is the first video chip from Intel with "serious" video 
decoding support.

Intel people feel free to correct me on that one.

> I believe that if Intel implemented full XvMC, the situation would be
> a lot better here for low end CPUs. For your application, it's a bit
> borderline. I have no doubt straight 720p or 1080i would play on your
> machine with XVideo out. I think you might run into trouble with the
> de-interlacing, however. I just am not entirely sure how the Pentium
> M compares to the Celeron D in terms of performance, nor have I
> evaluated the benefits (if any) of running my system entirely with 64-
> bit code. If you're going to be scaling down, you may be able to get
> away without any complex de-interlacing, eliminating the de-
> interlacing problem.


> This is what I wish I had known before I went forward with getting
> this hardware. I think if there is another chipset that supports full
> XvMC, it would be worth looking at first, as that's obviously going
> to be even lower CPU usage. There was a discussion some time back
> with Keith Packard mentioning this. At the time I bought the machine,
> I read the man page, it was a bit unclear and I got the impression
> that XvMC would work with the GMA 900. It does not. Intel has not
> released documentation nor drivers, which I found very disappointing
> and almost misleading, because the reason for purchasing their
> hardware was open source support.

There are some issues with XvMC in general, especially in open source drivers, 
because of the minefield that is otherwise known as multimedia patents. It's 
hard to implement this stuff fully without infringing on at least some 
patents, from what I understand.

> The only really good news I have here is that playback with XVideo -
> in every player - has been utterly flawless. None of the problems I
> hear about from NVidia users trying to use this.
> There is an interesting page here, although I'm not sure if their
> Intel GMA 900/950 XvMC support bit is 100% accurate:
> http://www.mythtv.org/wiki/index.php/XvMC
> If I were to do this again, I would look into Unichrome-based GPUs as
> they have potentially better acceleration support. I've not looked
> into them fully, but I would suggest you do before you make your
> purchase. And let's hope Intel gets with it and releases
> documentation or code to enable XvMC (or even better, XvMC VLD!) soon
> and lives up to their attempts to position themselves as open and
> appealing to open source users.

I think that Intel isn't going to release documentation, their open-source 
modus operandi has been to have their employees or their contractors (e.g. 
Tungsten Graphics) release the open source code working from closed 
documentation. This isn't exactly ideal, but at least they not only release 
open source code but they comment it and use symbolic constants, which is 
more than we can say for some graphics companies' open source drivers 
(*cough* nVidia *cough*). So you're best bet is to wait a few months while 
the Intel people work on the driver.

> And, if I am wrong on any of the facts I've brought up, somebody
> please correct me!
> -Galen
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Andrew Barr

Men go crazy in congregations they only get better one by one.
	-- Sting, "All This Time" (The Soul Cages, 1991)

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