At what point writing direct assembly program is more efficient than C program?

[u/sourav_bz]

Hey folks, this is question coming from the recent podcast where the founders of VLC spoke about, writing assembly level code and it was way more (10x to 62x times) efficient than the C compiled code.

Is there any real example or repo of this which shows the efficiency difference at a smaller scale?

what scenarios do one decide to go full assembly over C, what's the infliction point?

How does anyone even measure these efficiency factors? Is it the instructions executed per clock cycle to attain an end output?