[mythtv-users] XvMC -> DXVA equivalence?

Todd Ignasiak ignasiak at gmail.com
Fri Feb 24 02:37:29 UTC 2006

On 2/23/06, Bob <spam at homeurl.co.uk> wrote:
> Every now and then on the list, this page gets posted
> http://www.elecard.com/technology/dxva.shtml
> in threads about the hardware acceleration capabilities of various GPUs,
> with the explanation that DXVA is the Ms version of XvMC but that due to
> poor support from manufacturers, you won't get some cards to work under
> linux.
> But my nVidia Geforce 2 MX/MX400 while claiming to support DXVA with
> HWMC doesn't support XvMC, is this just nVidia turning it of in the
> drivers so I have to buy a new card, or does the MPEG acceleration under
> windows for this card use a different technology not available under
> linux?

I don't know if/why Nvidia turns off support in their driver.  But, the
older cards like your GeForce2 as well as the GeForce4 Ti cards, only
support the motion compensation portion of  DxVA/XvMC.    The GeForce4 MX,
GeForce FX, and newer cards support motion compensation plus iDCT.   Maybe
only the cards supporting full MPEG2 acceleration in hardware are enabled by
the Linux drivers.

The iDCT portion is the much more CPU intensive part of the MPEG decoding
offload.   I tried DxVA under Windows, with my GeForce4 4200 card (which
only supported motion compensation), and the CPU savings was not
noticeable.    With my GeForce FX 5200, XvMC with the full iDCT offload
takes CPU usage from 70% down to 40% on my Athlon64 3200+.
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