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How WinTV-USB Works
Video Overlay mode of operation
Live TV can be displayed on your VGA screen by using either the Video
Overlay or the Primary Surface mode. The mode which is used is dependent
upon your PC’s hardware and software. If your PC:
- has a VGA display adapter which supports Windows98 Direct Draw,
- and your VGA has a Video Port which is designed to accept digital video,
- and your VGA has enough display memory to hold the digitized video image
then ’s Video Digitizer “pushes” YUV 4:2:2 video pixels for temporary storage
into an off-screen part of the VGA memory called a Secondary Surface. This
method is called Video Overlay and DIB draw. The VGA display adapter
will then convert the video image from YUV 4:2:2 into RGB video and continu-
ously overlay the VGA screen with the video image. Using Video Overlay, the
VGA controller treats the live TV image just like any other window, which results
in a 24-bit video image on your VGA screen. You will also be able to display full
screen TV at all VGA resolutions.
VGA chips which have Video Ports include: the S3 Trio 64V+, S3 ViRGE
3D, Cirrus Logic 5446, ATI Rage II, Tseng Labs ET6000.
Primary Surface mode of operation
If your VGA display adapter has a Direct Draw driver but does not have either a
Video Port or enough memory to hold the video image off-screen, then the board
converts the YUV 4:2:2 video pixels into an RGB format which is compatible
with your VGA display adapter’s operating mode (8 bits per pixel, 16 bits per
pixel or 24-bits per pixel) and then moves the pixels directly into the display mem-
ory or Primary Surface of your VGA.
VGA chips which can support Primary Surface mode include: the S3 Trio 64,
S3 Vision 968, Matrox Millennium and Mystique and Tseng ET6000.
This results in a high quality video image whose color depth is dependent upon
your VGA display adapter’s operating mode. For example, your TV image when
running in a 256 color mode will not be as good as when running your VGA in
16-bit per pixel mode.
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