You will need to have on-board processing if you plan to go with real time processing and the low latency premise. There is no other way around it, since transmitting the signal will introduce sizable latency of an order of 200-500ms.
Consequently, I don't see how you can avoid loading your whole robotic vision system on top of your quad.
I believe that getting 1) and raw video isn't possible in an on-board format. Your best bet is something like this and you still don't get neither raw video nor guaranteed low latency.
I think your best bet is to combine a companion computer with a compatible camera. Consider the following combos:
- Get a raspberry pi with its very small digital camera
- Use the Odroid counterpart
- Do the same as the above in a BBB
The choice boils down to your hardware of choice, where you feel more comfortable programming.
Be warned though: Attitude control and split-second obstacle avoidance is not possible with today's board PCs and low FPS cameras. Very custom solutions are required to get the job done.
Edit: If you still want to go with Analog->Video conversion, something like this would be the hobbyist's option. PCI frame grabbers cost $$$. Still, I haven't used this particular product, so please do your own market research.