{HEAD ~ the second video} is provided in {TAIL ~ such a manner} that display/non display of the second video is switchable at an arbitrary point of time within 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 total playback time of the second video, 
is provided in
{ HEAD ~ the second video } is provided in { TAIL ~ such a manner } that display / non display of the second video is switchable at an arbitrary point of time within 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 total playback time of the second video ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL 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 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH