Current music recording and transmitting technology allows teachers to teach piano remotely or off-line. This is in many cases the only way to teach music, especially in rural or distant areas where the ratio of piano teachers to piano students is extremely low . MIDI recording technology allows a teacher to play a piano at one place and to see a piano played by itself, as by an “invisible teacher”, at another place (see Figure 1: the piano keys are pressed exactly at the same place, velocity and duration on a remote piano . However, to know how these keys were played by a teacher remains unknown. This includes the knowledge of which hand played a key, which finger was used, and who (in case of a four hand musical piece) was playing. With the current advances in computer vision and video recognition, some of this knowledge can now be also transmitted .