Wine GPU decoding

[Michael Müller]

Hi Henri,

 > Which APIs did you consider for this? What were the various issues?
 > What made you choose VAAPI in the end? Do you have tests for how the
 > dxva / d3d9 interface is supposed to work?

I mostly considered VAAPI and VDPAU for this as they both offer support 
for multiple vendors.

VDPAU has native support for nvidia, amd (only open source driver) and 
S3 but not for intel. There is a OpenGL backend for VDPAU which can be 
used on Intel graphic cards but I expect the video decode engine of 
Intel to reach a better performance than an implementation which is 
completely based on OpenGL.

VAAPI has native support for intel, crystal HD decoder, S3 and can also 
use VDPAU and the amds proprietary XvBA  interface. It simply supports 
everything VDPAU does plus Intel and the proprietary AMD driver. I think 
that a library which offers support for the most graphic cards is the 
best possible option for Wine as we do not want to implement these 
decoders multiple times.

The only issues I encountered so far with VAAPI is that not all backend 
support all commands and you sometimes get an unimplemented error. This 
is not a big problem in the most cases as you can use other commands to 
achieve the same, the only real issue I found so far is that the vdpau 
wrapper does not allow setting or querying for the native image format 
of a codec. I can force a yuv 420 format, but i can not set or query 
whether it is stored as NV12 or YV12. When mapping the image it is 
possible to define a image format but I don't know whether a 
conversation is done or if is the raw decoded data. It may be necessary 
that we actually take a look at vdpau library and hard code some values 
if the vdpau backend is used to avoid conversations between formats.

There are currently no tests so far. The reason for this is that mingw 
does not support the dxva header files and you can not use the hardware 
decoder in a VM. So I basically wrote some test code in MSVC and tested 
it on an old laptop which is running Windows 7 with a nvidia 9800 GTS.

VLC wrote some header files for mingw which they use to cross compile 
VLC, but it does not offer everything we need ( 
http://www.videolan.org/developers/vlc/modules/codec/avcodec/dxva2.c ). 
Maybe whe can use the wine header file or ship a more complete version 
to allow cross compiling.

If you want to know how dxva2 is used by applications I would suggest 
you to take a look at these 3 files used by VLC  to decode mpeg2 using 
dxva2:

http://www.videolan.org/developers/vlc/modules/codec/avcodec/dxva2.c
http://www.ffmpeg.org/doxygen/1.0/dxva2__mpeg2_8c-source.html
http://www.ffmpeg.org/doxygen/1.0/dxva2_8c-source.html

VLC initializes DXVA2, creates the surfaces and passes them to avcodec 
for decoding and storing the result images. Since you need a complete 
mpeg2 bitstream decoder to gather the information for decoding it is not 
very easy to create a small example code.

@Stefan Dösinger: I will try to do some tests this evening when I am at 
home.

Michael