This is a fabulous parody that will have you in stitches if you've ever known any singers.
My favorite lines include "A scale is something... it's on a piano... it's the notes of a piano," and "Singing higher... you lift your eyebrows up like this... and lift your chin." Classic!
I love how developed her character is, from how she pronounces the words "sing" and "singer" to her facial expressions. She's put up a bunch of other videos of her "Miranda" persona singing, like this hysterical rendition of the National Anthem, which seems to be in about three dozen different keys:
Lest you think she's seriously attempting good singing in these videos, I think she's actually a real singer - "Miranda" appears to be the alter-ego for Colleen, who has several singing videos here.