Video tape recorders have two ways of recording-longitudinal as on ordinary audio tape recorders, and there is a transverse called high-fi with FM modulation.
Longitudinal recording on the tape is written by a separate audio head, which is in a static position, the quality of such recording in the frequency range of 50-15000Hz on average.
High-file audio recording is made by heads installed on the drum, there are two audio heads, they have nothing to do with video heads, which are also installed on the drum.Recording by such audio heads is made standard 20-20000Hz and dynamic range of 90Db.
So these video heads were disconnected at all, only two (each per channel, left and right) audio heads are functioning.
I'm talking about the video tape recorder shown in the video, it's S-VHS format.
But there is a format Betacam SP, in this format the same heads record audio and video, it will not be possible to disable the video signal when recording.
I wrote above that the video signal is recorded over the audio and partially destroys the audio signal, in the case of disabling the video signal this does NOT happen.
Of course I am only interested in those formats that record ANALOGOUS signal.