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About Video Capture solution,
Basicly,you need a Video decoder to covert Analog Video to Digital Video YCbCr,you can visited Philips web-site SAA7115,SAA7118,SAA7114.....
Then You need a FIFO to store the image (for example Averlogic AL440....) Then you can use a micro control to read from fifo then transfer to RS-232 !
I know it is not eaxctly what you want, but a serial port or a parallel port is not fast enough. Even with a PCI card, capture is not obious unless you reduce the resolution or frame rate or you have a very fast PC.
If you have an ATI video there are an 8-bit parallel video port on the card that allow you to connect a BT848 or Phillips chip and control them through I2C... There is an SDK on ATI's web site for this.
Guys are right, you can not use rs232 or printer port for this job.They are too slow for this Try to use usb port.You can find usb chips at www.ftdi.com For video capturing you can use booktree chips and also you should use fast mcu's like atmel's or pic's new mcus'.
in my opinion, the interface to host will depend on what application you are targeting. if you only want real time image capturing to your PC, you definitely need a fast comm. link. Basically, the speed of the data link must be greater than frame resolution*frame size*frame rate, of course, plus some overhead.