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Old 30th January 2003
bluedan bluedan is offline
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Overlay is a nifty solution to provide quick picture composition on screen, without raising CPU load much. The GPU on your graphic board does most of the work.
Overlay can be created in different formats, i.e. color space formats.
If you're eager to learn more on that have a look here:
Most important for quick overlay drawing are YUY2, YV12 and UYVY.
These color space formats differ from RGB (RedGreenBlue) color information storage in that way that they only distinguish between a luminance (brightness) and chrominance value.
They are generally speaken faster.
YV12 is the fastest AFAIK, but causes some trouble with cards which however don't properly support this format, thus image quality is decreased. For instance Matrox cards as well as NVIDIA are said to have bad driver architecture, bad overlay support. But, I own one myself (TNT2) and never had difficulties.
YV12 is usefull on slow machines for MPEG4 decoding (DivX and XVid) is heavy work for CPU, so every off-load is "good".
You can try to switch it on in bsplayer trough overlay mode 1, though curiously you will get YUY2 anyway when your XVid/DivX resides in an OGM container (instead AVI). Cannot explain.
If you switch to bsplayer overlay mode 2, you'll get YUY2 output which is default and preferred overlay output from most players and DirectShowFilters (ffdshow !).
On modern graphic cards there ought to be no visibile difference.
Changing between those two modes is only advised if your card does not support one mode. Also it's better to not manipulate this during playback, some systems don't tolerate this and bsplayer crashes. After mode switch close player and re-open to make it store overlay initialisation info in registry.
To find out which color overlays your graphic system supports try to use Sisoft Sandra 2003 to find out:

Unfortunately, I feel helpless myself with bsplayer sometimes being unable to create overlay surface.
If there's a second application running using overlay, ok, but sometimes it just fails right after start-up. :shock:
Maybe BST can explain some day...

Hope this explained a bit!!
Keep forum organized and use the search button !! :o
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