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.)
I think that makes it easier for those who are math brained and not creative brained. To understand music theory fully, you need that creative brain. Because we aren’t even talking about resonance harmonics, triplen, or any of the crazy interharmonics.
edit
actually watching again, at the very beginning, he demonstrated resonance harmonics.
If the fundamental is 100hz, then the 1st harmonic is the fundamental (100hz), the 2nd harmonic is 200hz, the 3rd harmonic is 300hz, and so on.
Sometimes the harmonics aren't exact. On a piano, if the fundamental is 100hz then the 2nd harmonic might be, say, 200.1hz or something. Some inharmonic instruments like gongs aren't anywhere close to the "ideal" harmonic series.
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.)
edit
actually watching again, at the very beginning, he demonstrated resonance harmonics.
It's not actually "N times", isn't it?
Sometimes the harmonics aren't exact. On a piano, if the fundamental is 100hz then the 2nd harmonic might be, say, 200.1hz or something. Some inharmonic instruments like gongs aren't anywhere close to the "ideal" harmonic series.