Best way to convert PAL analog input video to jpeg or mpeg using arduino

Hi, this is my first arduino project and I have searched through hundreds of web sites looking for some sort of shield to equip to my arduino to take in PAL analog video and convert it to jpeg or mpeg so as to save on to an sd card at a later stage. What would be my best approach to doing this? If there is no middle man device, how would I go about beginning to program it?
Kind Regards,
Liam

The reason you have found little or nothing about using Arduino to convert PAL (composite?) to jpeg/mpeg is it's not something the Arduino can sensibly do. The best you could hope for is to use something like this or this (but PAL versions) and store the jpeg still image to SD card. Forget about anything mpeg though, for that start looking at something like the Raspberry Pi