Home » Developing U++ » U++ Developers corner » What (or if) format of video buffer would be needed for video support?
| What (or if) format of video buffer would be needed for video support? [message #10705] |
Mon, 23 July 2007 23:02 |
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fudadmin
Messages: 1321
Registered: November 2005
Location: Kaunas, Lithuania
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Just some research to feed some imagination for the future... 
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DVD quality MPEG2 is in YCbCr 420. Many broadcast quality mpeg2 videos are coded in YCbCr422 or even YCbCr444.
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from: http://thread.gmane.org/gmane.comp.graphics.agg/2466/focus=2 486
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after various tests, I have implemented the YCbCr support in my application
to my satisfaction. It turned out that it didn't make much sense to support
YCbCr422 directly by a pixel format class. It is better to use a YCbCr444
buffer in main memory, rendering any vector stuff on top of that and then
converting to YCbCr422 on the fly while blitting to graphics memory for use
by the overlay engine. Since writing to graphics memory is slow, the
additional filtering overhead is neglectable. (If bandwidth is not your
concern, your graphics card overlay engine is likely to support YCbCr444
directly.) This is all much faster then trying to use YCbCr422 directly
paying attention to odd and even pixels let alone trying to filter in the
pixel format implementation. The pixel format implementation for YCbCr444 is
virtually the same as the implementation for RGB24. The only difference is in
the color representation. One could use a fake agg::ycca8 color type that
uses "r g b a" as the names for "y cb cr a" so that one can directly use the
rgb pixel format and image filters. In the "ycca8" color type implementation,
one would convert into YCbCr color space like so:
inline void
rgb_to_ycbcr(value_type r, value_type g, value_type b,
value_type& y, value_type& cb, value_type& cr)
{
y = (8432 * r + 16425 * g + 3176 * b) / 32768 + 16;
cb = (-4818 * r - 9527 * g + 14345 * b) / 32768 + 128;
cr = (14345 * r - 12045 * g - 2300 * b) / 32768 + 128;
}
// ...
ycca8::ycca8(const rgba8& c) :
a(c.a)
{
rgb_to_ycbcr(c.r, c.g, c.b, r, g, b);
}
void ycca8::clear()
{
y = 16;
cb = 128;
cr = 128;
a = 0;
}
// ... and so on
r, g, b and a being members of ycca8 really meaning y, cb, cr and a.
Given these findings, is there still interest in my YCbCr stuff... or do you
have any comments or further insights?
Best regards,
-Stephan
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So, my questions is: Would YCbCr444 (or any other) video buffer(s) needed as a starting point for U++ video support?
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