Re: OT: Why is usb data many times the cpu hog that firewire is?

Paulo Marques
2005-02-21T19:28:41Z

Gene Heskett wrote:
> On Monday 21 February 2005 12:58, Oliver Neukum wrote:
>[...]
>>A video stream over usb1.1 must be compressed due to bandwidth
>>available. Decompression needs cpu.
>>
>
> Thats what I was afraid of, which makes using it for a motion detected
> burgular alarm source considerably less than practical since the
> machine must be able to do other things too. Darn. And its usb1.1
> even when plugged into a 2.0 capable port.

Depending on the camera model you can try some bandwidth reduction
measures to try to make it send uncompressed video:
- reduce frame rate. Something as low as 2 fps should be enough for
motion detection.
- reduce requested resolution. This of course depends on whether you
have enough resolution or not.
- selecting gray scale images. I don't know if your motion detection
software is greatly affected by this, or not.

USB1.1 bandwidth is enought for 640x480, 8 bits gray scale (or color, 8
bits bayer pattern), at 3 fps.

Of course, you can always buy a USB2.0 camera :)

--
Paulo Marques - www.grupopie.com

All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke (1729 - 1797)