I tried Tangmo solution 1 to synchronize audio and video.
I had to bring out the PC audio and the piano as well as in the headphones also on the speakers during the recording.
Also on the speakers so that audio (backing + leave piano) could be recorded through the microphone of the Web Cam.
It would have been much simpler to record the audio output of the PC directly through the Stereo Mix device which I do not have and cannot make appear in Win 10 recording devices
My mobo has an integrated sound card and is a bit old and there are no more updated drivers for Win 10.
I'm thinking of buying a SoundBlaster and putting it in a free slot on my PC: Anyway, by bringing the audio on the external speakers I managed to achieve the aim.
I also exalted Biab's count-in by beating in sync with it with a spoon on a pot :-)

Thank you all.

Last edited by cubalibre; 05/23/20 05:23 AM.