it's 24Hz to be able to match with your eyes own resolution, i thought eyes only "took a picture" 24 times a second so there is no need to have more, more than 24Hz just means there are frames you don't even get to see.
and if that is true about repeating every 4th frame for 30Hz then that is just silly, i mean that would actually make a jitter as much as having less than 20Hz.
i could be wrong about 24Hz because i vaguely remember it being only 20 pictures per second for the eyes.
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kind of off-topic: i remember seeing/reading something about pigeons eyes taking about twice as many pictures per second as human eyes (i assume it's the same for most animals that are considered to have better eyesight than humans) so watching a cinema screen to them is like us watchinga slide show.
