[mythtv] thoughts: using XvMC as a generic mpeg2 decoder?

Ben Osheroff ben at gimbo.net
Tue Apr 24 18:15:02 UTC 2007

Daniel Kristjansson wrote:
> On Tue, 2007-04-24 at 00:23 -0700, Ben Osheroff wrote:

>> I've been thinking of writing a little test program that tries to dive
>> down into the private_data XvMC pointer and pull out the decoded MPEG-2
>> content before the nvidia driver pushes it to the screen.  If it worked,
>> it'd be effectively offloading content decoding to the card, and you'd
>> be able to apply filters and all that good stuff before actually drawing
>> to the screen using XV.
>> I have no idea if this will work.  I suspect not, and if anyone has
>> already tried this and failed, please let me know before I embark on a
>> fool's errand.
> When you enable the xvmc opengl output method it copies data
> from the xvmc surface to an OpenGL texture, which you can then
> process using OpenGL fragment programs to do filtering. Trying
> to copy the data from video card memory to system memory won't
> work, the AGP/PCI bus is too slow and memory protections will
> get in the way of any user space program doing this as well.

ok, perhaps I will look into that method.  Just to be clear on what
you're saying:

The renderer on the nvidia/ati card never actually renders a frame into
system memory, but you can write filters in openGL that will run
directly on the video card's GPU/memory?

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