Less of a complaint and more of an observation — it is great that you can select inverted X/Y individually for basically every situation in MP4.

It's probably negligible for smaller lengths, but I imagine Array.sort would be faster over a certain limit (stdlib throws out 100,000 as an example) — worth benchmarking when n gets large, but I usually don't worry about it.

There was a somewhat infamous testing year that used audio from Neon Genesis Evangelion — but forget exactly when

I "trained" for the JLPT N1 by listening to anime audio without video (mostly in the car) — particularly 四畳半神話大系.

I always thought listening was hard, but most people I talk to think it's the easiest part of the JLPT, so ymmv.
That nearly perfect on the reading will probably do a lot to help!

Maybe that's why it's great for writing compilers? I wouldn't know.

(Though I did start with a generic "let rec loop" before I realized I did not need as much flexibility.)

The humble fold:

Array.sort compare ranges ;
Array.fold_left
(fun a (min1,max1) ->
match a with [] -> (min1,max1)::a | (min0,max0)::tl ->
if min1 > max0 + 1 then (min1,max1)::a
else (min0, max max0 max1)::tl) [] ranges |>
List.fold_left (fun a (rmin,rmax) -> a + rmax - rmin + 1) 0

"The illusion of choice" meme.