Re: external video capture

John Carey (john@carey.com)
Tue, 7 Mar 1995 22:47:10


Lisa,

A modem and a video caputre card are very different things. An external
modem makes use of an existing serial port on a computer while an internal
modem usually contains an additional serial port as part of its circuitry.
Neither of these devices require particularly fast data transfer since analog
phone lines offer a de facto bit rate cap.

Video is quite a different matter. Video requires a very high speed data bus.
All video capture schemes with which I am familiar take some sort of video
signal from an external source such as a camera or a video tape player. They
digitize the incoming video signal and using the internal bus structure, send
the bitstream to the hard disk or to RAM as fast possible. I know of no
mechanism for bus speed data transfers from a device external to that bus
structure. The Connectix Quick Cam is an exception to this rule, and it
suffers from pretty dismal performance with regard to internal buss oriented
solutions.

Please, no flames from happy Connectix users. I believe that it is a good
product, especially when cost is taken into consideration, but a serial port
just isn't quite up to the task, nor are parallel ports particualrly suitable
for high quality video capture. I can imagine a possible product which used
the pcmcia port, but it would be a little unweildy in that it would have to be
much larger than the average pcmcia card to contain the ram buffers and
digitizing chip set. Even then, the pcmcia is hardly a high speed bus.

Connectix is making noises about producing a PC version of their product and
if you are looking for a portable PC based low quality video conferencing
system, perhaps the QuickCam for PC combined with CU-SeeMe and a ThinkPad will
do the job for you.

John (john@carey.com)

In article lmv1@cornell.edu (Lisa Mariko Vasquez) writes:
>Date: Wed, 8 Mar 1995 00:11:45 -0500
>From: lmv1@cornell.edu (Lisa Mariko Vasquez)
>Subject: Re: external video capture

>by external video capture, i mean a video capture board that does not need
>to be installed in the innards of a thinkpad which wouldn't accept it to
>begin with--like an external modem as opposed to an internal modem.