I'm a little bit confused what exactly all the values of the Uint8Array retured by getByteFrequencyData() mean/represent?
How can I understand their value? And why are most of the first values defined and the later ones are most 0?
The latest spec explains getByteFrequencyData in more detail. Basically, it's the magnitude of the FFT of the data converted to dB and scaled to a byte value between 0 and 255. If the later values are 0, it's because there is very little frequency content there.