On Tue, Jun 27, 2000, Roger Hardiman <[EMAIL PROTECTED]> wrote:
> 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)
Actually, the low speed is 1.5 megabits.
If the device is low speed, it can only do certain transfers, such as
control and interrupt. It is not suitable to stream data to the host.
I've only seen keyboards and mice that are low speed. Most other devices
are high speed.
> 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
Most USB capture devices do a and c. With b as a fall back.
JE
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