wherein {HEAD ~ metadata} manages the time at which the displayed area of the second video is changed to {TAIL ~ a different position} in the first video, 
wherein { HEAD ~ metadata } manages the time at which the displayed area of the second video is changed to { TAIL ~ a different position } in the first video ,
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH