the second video is provided in such a manner that display/non display of the second video is switchable at an arbitrary point of time within {HEAD ~ a displayable period} designated in the first video, the displayable period representing a time range of the first video that allows the display of the second video and the displayable period being longer than {TAIL ~ total playback time} of the second video, 
the second video is provided in such a manner that display / non display of the second video is switchable at an arbitrary point of time within { HEAD ~ a displayable period } designated in the first video , the displayable period representing a time range of the first video that allows the display of the second video and the displayable period being longer than { TAIL ~ total playback time } of the second video ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH 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