{HEAD ~ a synthesizing portion} for laying and synthesizing {TAIL ~ the second video} over the displayed position inside the first video, designated by the designating portion, 
for synthesizing
{ HEAD ~ a synthesizing portion } for laying and synthesizing { TAIL ~ the second video } over the displayed position inside the first video , designated by the designating portion ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH