It may seem like a strange question, but I wondered if anyone had an answer.

I see people capturing at all sorts of strange frame rates, and I can't really understand the logic behind it. By my thinking, you would never capture at anything but the source frame rate.

As I imagine it, the capture chip on your card (eg Philips SAA7113, BTwhatever etc.) will capture fields/frames at the rate specified by the format (PAL/NTSC etc) that it detects. So for PAL, for example, it will capture at 25fps. This is controlled by the video signal sinc pules etc.

So, when you select another rate in the driver, what happens? Does the driver have to manipulate the data to 'synthesize' the chosen frame rate? (eg throw some frames away). Or??