seoul footage release last week north korea purport show fire submarine-launched ballistic missile slbm appear fake accord study u.s. experts defiance u.n. ban north korea say ballistic missile technology would allow launch nuclear warhead submarine though analysis north korean state media image cast doubt claim north korea release submarine launch footage separately conduct fourth nuclear weapons test last wednesday north korean state television air footage friday submarine test say take place december unlike previous slbm test may announce time south korea military say saturday north korea appear modify video edit scud missile footage 2014 although official tell reuters ejection technology might improve since may test analysis california-based jam martin center nonproliferation study cns show two frame video state media flame engulf missile small part body break away rocket eject begin light fail catastrophically melissa hanham senior research associate middlebury institute cns say email north korea use heavy video edit cover fact hanham say north korea state media use different camera angle edit make appear launch several continuous launch fact single event north korean propagandists use rudimentary edit techniques crop flip old video footage early slbm test scud missile launch cns study show analysis 38 north monitor website john schilling aerospace engineer specialist satellite launch vehicle propulsion systems say appear video launch conduct submerge barge rather submarine fail launch combine test barge show north korea still long way go develop system say initial operational capability north korean ballistic-missile submarine expect 2020 north korea claim recent nuclear test advance powerful hydrogen bomb draw skepticism u.s. government experts remain unclear north korea develop nuclear device small enough mount missile north korea fake missile test footage u.s. experts