SDL YUVOverlay Zoom question

I am using SDL YUVOverlay function on my framebuffer .
my method is as following :
copy data to overlay
displayyuvoverlay(overlay ,&dst)

I found that with the increase of “rate” , the
performance of it become worse and worse.
I have test it and get some data :
for a 352*240 yuv files, fps(frame rate per second)
when rate =1/2 fps=650
when rate=1 fps=635
when rate=3/2 fps=300
when rate=2 fps=54

because I want to use SDL to play realtime video ,
when I wanna a bigger display , I have to drop frames
So I want to know how even somebody can use full
screen to display the movie . How they get it ?

On the frambufer ,It seems I cannot use HW_Surface .
why ?
Any hint can give the better performance when using
yuvoverlay zooming ?__________________________________________________
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Check the hardware flag of the overlay:

If you aren’t getting a hardware overlay, there isn’t much that can be
done to alleviate the sharp performance degradation as you scale. You
can always go in and hand-optimize the scaling, smoothing, and
colorspace conversion code. While this is already MMX tuned, you could
try SSE or other optimizations, but you’ll never come close to what
hardware acceleration typically does.

Oh, and as always, check your drivers, and software, etc and make sure
everything is up-to-date or in a working state, if you think you should
be getting hardware acceleration but you’re not.

I forgot to mention that the regular SDL window should be filled
with black. That is the default, but just in case you are changing it
someplace. On some systems you need that particular fill color in the
window for the hardware overlay to kick in.


What is required to get hardware overlay ?
Every time I print the value of overlay->hw-overlay ,
I just get 0; Even on xwindow , I still get the same
result .
Why ? Does it relate to video card type ?
My video card is nvidia riva tnt2 . Doesn’t it
support hardware overlay ? Then what type can be
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