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