Hi,

The PIC lives in a digital world where evrything is between 0v and 5v. Video lies in the analogue world, a strange and wonderful world it is too... But everything in analogue video does not live within the 0v to 5v parameter.

Video feeds are often AC coupled through a capacitor and require an amplifier and a DC clamp circuit before they can be sampled. Easiest way to interface to video is to use a dedicated sync seperator which can perform all the analogue processing and output into the digital domain. Take a look at National LM1881 for example.

PAL video sync is 300mV with the video sitting a further 700mV above that. Total amplitude is 1v peak to peak. The sync is a composite sync containing short pulses for line sync, longer pulses for frame sync and equalising pulses between the two. There is a good description of video sync structure in the LM1881 data sheet.

Tim.