It’s also not very intensive, especially since video decode usually runs on the GPU.
(Or it should - browsers are not always very good about this but the tools are there, they just don’t want to pay licensing fees to use them.)
I always cringe a bit when people insist they need 6 cores “so they can have discord and Spotify open while they game”. People don’t generally have a very good intuitive sense of just how little cpu time it takes to run those (a lot of times the “at the desktop” measurements are not even with the processor clocked up, it’s running in the lowest active power state), and there is almost always a little cpu headroom due to non-perfect game scaling. Context switching is cheap, your OS is running thousands of threads at any given time, but people don’t have a good intuitive sense of the overhead of context switching either.
Playing a video and writing a document is something that can be trivially done on a core2duo era processor, or the modern equivalent of a low-end dual-core nuc with e-cores (atom cores) like a J4005. You don’t even need performance cores for that.
The tradeoff Intel is making is that some tasks need performance cores because they can’t really be parallelized all that well, and embarrassingly parallel stuff is more efficient to implement with lots of smaller cores. In principle this is also more power efficient, like big.LITTLE in phones, but Intel actually seems to have fairly poor power scaling - they are space efficient but not all that power efficient. This is also partially due to the fact that the little cores share a core voltage with the big cores - the big cores need higher voltage to clock up and that kills efficiency on the little cores. At that point you may as well clock the little cores up too since they have to share the voltage anyway, and that’s an inefficient way to run them.
As Agner Fog mentions, the AVX-512 is also present in silicon yet disabled, which hugely blows up core size for almost no benefit (it’s dark silicon which does have some minor thermal benefits). Alder Lake is in many ways not that well-designed at a high level, but it is magnificently fast on those performance cores and the e-cores would be very nice if they weren’t conjoined awkwardly to the p-cores. Gracemont-based server and atom chips are going to be nifty when they finally arrive.
Apple is still way ahead with Icestorm though - those cores are absolutely absurdly tiny for the performance they give. They are 0.5mm2 each iirc, even considering the node shrink that is teeny-tiny, they are half as many transistors as a Zen3 core and almost the same performance (meaning much higher IPC) or something along those lines. Firestorm is neat but Icestorm didn’t get nearly the attention and it is really insanely fast for how few transistors it uses.