Video Protocol Without Required Speed
I was able to do NTSC vídeo back in 1987 with a 68000 8MHz microprocessor and just a couple of timer peripherals and an ADC, via interrupt handlers with enough processing power left over to make it comparable to the more common microprocessors at the time. 

I remember Hackaday projects of at least a decade ago in which they use PIC 18’s to do similar things. 

You have considerably more processing power available in the Arduino platform (including DMA), not to mention those that already have some video support built in.