[PD] hd video in gem on linux

[chris clepper]

On 12/8/06, marius schebella <marius.schebella at gmail.com> wrote:
>
> Hi,
> I want to use Gem to synchronize several linux machines playing high
> resolution videos 1440x1080 or 1920x1080. any comments on that???
>
>
I do a lot of HD work using GEM on the Mac now and here is what I find most
effective:

1) Lossy intra-frame but not inter-frame codec.  JPEG based ones including
DVCPRO_HD are the ones to use.  Data rate will be around 100Mbit which
standard SATA drives easily handle.  The codec needs a ton of SIMD code and
multiple threads for decompression.

2) Decompression to the appropriate video color space.  4:2:2 YCbCr (YUV) is
the way to go.  Conversions to RGB on the CPU are going to kill any
efficiency.  YCbCr textures are half the memory size of RGB ones too.

3) Support for YCbCr textures in the OpenGL drivers.  Upload as YCbCr and
let the hardware convert the colorspace.

4) DMA texturing path with no extra caching and memory copies of the texture
data.  By default the driver keeps one or more copies and the routines to
make the copies are often slow.  Also, the card may keep copies too but that
is less of a problem.

For #1 libavcodec has some fairly efficient paths for MJPEG and MPEG2 - the
former is probably the faster of the two although try I frame only MPEG2.
The libavcodec will also deliver #2 but you are out of luck for #3 because
ATI/Nvidia don't have any support for YCbCr on Linux or Windows so neither
#2 or #3 work.  Finally, #4 doesn't seem to be possible using the usual ATI
or Nvidia drivers although there is supposedly a way to do fast texturing on
Nvidia, but I haven't gotten it to work yet.

That 1 out of 4 score is what keeps most of my paying work on the Mac for
now.  I am working on getting Windows up to speed which could have the
byproduct of making Linux faster too since the GL drivers are pretty much
the same for Nvidia.
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