if you want to spider-web your apple with 30 gauge jumpers maybe you could only do low rez then yes, but your still sampling the video data and then post processing it to output, so you need memory or the screen will flicker

I am using a ATmega 328, which is the same as he is using, at a high res image monochrome, 1 bit per pixel your looking at about 8k of ram at 256x256, the apple does 290x192 in colour, either way the mcu has 2k of ram, adding extra ram slows down the mcu for communications, and its already using assembly language to barley put out vga sync signals and whatever is left is used for 40 col graphics in colour if your slick on code

so you need more cpu and more ram and it snowballs

you could do it line by line, but its the same deal but you need a ton more speed, and stuff that has more speed usually has enough ram to store a sample, and at those speeds its just easier to decode the analog signal and resample it, plug n play style

its not expensive or anything, it just a large project for a small audience