[Mesa-dev] hardware xvmc video decoding with nouveau

Maarten Lankhorst m.b.lankhorst at gmail.com
Fri Jul 29 06:37:19 PDT 2011

Hi guys,

With some help from the nouveau team I managed to get video acceleration
working for my nv96 card. The video buffer api works well enough for nouveau,
I added flags to vl_video_buffer_create_ex so I could force a linear surface
with a nouveau specific resource flag, which I only specified when hardware
that potentially supported hardware decoding was found. With the video
buffer API, I only needed to specify that and I could get it to work.
This made it easy for me, I only had to write code to talk to the decoder.

The api for implementing the decoder I'm less happy about. I know this is
because there is no real support yet for other decoders, but I think
pipe_video_decode_buffer api is wrong right now. It assumes that the
state tracker knows enough about how the decoder wants to interpret the
The nouveau hardware decoder has to interpret it in it's own way, so that
makes it need a different api. I think the best thing would be to pass
information about the macroblock with a pointer to the data blocks,
and then let the decoder buffer decide how to interpret it. Also is it the
intention to only start decoding when XvMCPutSurface is called? If the
reference surfaces are passed, I can start decoding in XvMCRenderSurface.
I'd also like it if flush_buffer is removed, and instead the video buffers
are passed to end_frame.

Some of the methods to pipe_video_buffer also appear to be g3dvl specific,
so could it be split out?

I was thinking of something like this for pipe_video_decode_buffer, with
flush_buffer in the decoder gone:

struct pipe_video_decode_buffer
   struct pipe_video_decoder *decoder;

   /* Should not leak even when begin_frame was called */
   void (*destroy)(struct pipe_video_decode_buffer *decbuf);

   void (*begin_frame)(struct pipe_video_decode_buffer *decbuf);

   /* *ONLY* called on bitstream acceleration, makes no sense to
    * call for XvMC, this allows it to be set to NULL */
   void (*set_quant_matrix)(struct pipe_video_decode_buffer *decbuf,
                            const uint8_t intra_matrix[64],
                            const uint8_t non_intra_matrix[64]);
   /* Same story here */
   void (*decode_bitstream)(struct pipe_video_decode_buffer *decbuf,
                            unsigned num_bytes, const void *data,
                            struct pipe_picture_desc *picture,
                            unsigned num_ycbcr_blocks[3]);

   /* Can be NULL when bitstream acceleration is used.
    * Append a single macroblock to the list for decoding */
   void (*decode_macroblock)(struct pipe_video_decode_buffer *decbuf,
                             struct pipe_video_macroblock *mb, short *datablocks);
   /* If end frame is not set, it means more macroblocks may be
    * queued after this, and this is just an intermediate render,
    * if its beneficial to do so. Otherwise just return without
    * doing anything.
   void (*render_frame)(struct pipe_video_decode_buffer *decbuf,
                        struct pipe_video_buffer *frames[3],
                        bool end_frame);

Comments are welcome. The functions I removed should probably just be moved
to a g3dvl specific struct vl_mpeg12_video_decode_buffer.

If you feel like testing xvmc with a capable card, I put my tree at
http://repo.or.cz/w/mesa/nouveau-pmpeg.git .

I attached 2 patches, 1 is to clean up xvmc/test_rendering.c, the other allows me to 
specify a custom flag to force a linear surface. Should be mergeable right now.

Special thanks to calim and mwk for their patience and help and to jb17bsome for the
original code which I based this on, even though this code is significantly different
from the original. :)


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