[MPlayer-dev-eng] Question regarding MPlayer's OpenGL output

[Reimar Döffinger]

On Wed, Oct 19, 2011 at 11:32:40AM -0400, Mostapha El-Shafey wrote:
> The reason I'm asking is because I'm developing an application (in Qt) that
> displays many (up to 20) video streams at once and it is required for the
> video display to take up as little CPU time as possible. By my simple tests
> it looks like MPlayer is doing something right, OpenGL-wise. I went through
> the vlc code and what it seems to do is just create a quad with a texture,
> while it looks to me that MPlayer is using pixel buffers, glMapBuffer() and
> glUnmapBuffer(). Problem is I tried using pixel buffers in my application
> but it doesn't make a difference in terms of performance so I must be
> missing something MPlayer is doing.

The PBO code isn't usually used I think, it doesn't make all that much
difference.
However if you used PBOs naively you'd probably get atrocious
performance, depending on the hardware and driver version you need to
have the right line stride, input format etc. etc.
Depending on what kind of memory you get you should also be careful
which memcpy code you use, for AGP memory SSE2-based copy can have
issues and be a good 10% or more slower that SSE one.
But are you sure it's not just that you are pushing RGB textures, which not
only means you have to do the YUV->RGB conversion in software first but
also requires almost 3 times the bandwidth?