> * overlay flavour 1: by some magic way, the card grabs directly to the
> video ram and without cpu intervention, the image is refreshed (in RGB mode
> I think). It must cause a slight performance loss though because the bandwidth
> on PCI bus is not infinite (try putting four TV cards to see what happens).
> [how does that thing scale???]
Two schemes
#1 TV card dma drives an offscreen YUV buffer and the video card scales
converts and overlays. This is preferred - less PCI bandwidth and arbitary
scalers
#2 TV card does RGB conversion and scaling
> * overlay flavour 2: XvImages and friends; here the card grabs to a special
> shared memory segment (can be in YUV format). The image is not converted
> to RGB before sending to VGA, and is hardware scaled.
> I can't see a valid reason to use this one (which requires a X4.0.1 setup)
> compared to the previous.
This is mostly useful for mpeg/dvd playback. It helps if the hardware on the
capture device cannot do overlay too
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