A minor terminology quibble: the video refers to the Nth harmonic as if it's the fundamental frequency times N+1, but it's usually fairly standard to refer to the frequency that's N times the fundamental as the Nth Harmonic. So, the fundamental is the 1st harmonic.
For overtones, there's less of an established standard, but usually the 1st overtone is twice the fundamental, the 2nd overtone is 3x, and so on. (I tend to avoid talking in terms of overtones because of the ambiguity.)
