Here are some more maths for Video and USB.
USB
===
This has 2 speeds,
2 megs bits per second (approx 0.2 Megabytes per second)
12 megs bits per second (approx 1.2 Megabytes per second)
NTSC Video
==========
TV cards grab NTSC as 640x480 pixels, 30 fps
(PAL is 768x576 pixels, 25 fps)
Lets take RGB first. 3 bytes per pixel (for 24bit colour)
640x480 x 3 x 30 bytes per second which is
= 27 Megabytes per second.
If you use YUV with a subsampled U and V plane
a good image can be captured in 2 bytes per pixel
640x480 x 2 x 30
= 17.5 Megabyres per second.
PAL is 32 Mega bytes per second (RGB) and
and 21 Mega bytes per second (YUV)
SUMARY
======
USB is 1.2 Megabytes per second
and NTSC video (uncompressed) is 17.5 Megabytes
per second.
So, to get any video over USB we need to
a) drop the resolution
b) drop the frame rate
c) apply video compression over the USB wire
Roger
) NTSC resolution is 640x480 pixels.
> > Think about it.
> I have encountered with this rating, but where it from ?
> IMHO 8MGhz (2*video frec) * 3 bytes (RGB 24bit per point) = 24Mbyt/sec.
> But in reality there is transfer with YUV values that consume 1 byte
> per point and since about 8Mbyt/sec.
> Please point me to where i am wrong.
>
> Thanks
>
> Andrew
>
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--
Roger Hardiman
Strathclyde Uni Telepresence Research Group, Glasgow, Scotland.
http://www.telepresence.strath.ac.uk 0141 548 2897
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