One hard part is that on the youtube side, most views occur within the first 48 hours or so and a good fraction occur within the first 6. With netflix, they have a catalogue of ~5000 videos and gets <200 new per month. Youtube has around 30k channels with more than 500k subscriptions, so that's somewhere around 30k videos per week.
But yeah, once your hot data size exceeds cache byebye efficiency