ios - Shorten/edit video recorded as AVCaptureMovieFileOutput with fixed time -

in app recording video using device's camera , avcapturesession save. long story short, need able cut out first x seconds of recorded clip. not want user presented 'edit video'-view, , not "fixed" amount of time per say, @ end of day, left here cmtime value of how have cut out beginning of clip. have been looking @ avassetwriter etc, no luck. playback, guess [player seektotime:time]; do, need actual video time duration shorter, cut out beginning. method, or can documentation this?

have tried avmutablecomposition? have processing time though. like:

// asset avasset *asset = [avasset assetwithurl:yoururl];  // asset tracks avassettrack *assettrackvideo = [[asset trackswithmediatype:avmediatypevideo] objectatindex:0];  avassettrack *assettrackaudio = [[asset trackswithmediatype:avmediatypeaudio] objectatindex:0];  // create composition avmutablecomposition *composition = [avmutablecomposition composition];  avmutablecompositiontrack *trackvideo = [composition addmutabletrackwithmediatype:avmediatypevideo preferredtrackid:kcmpersistenttrackid_invalid];  avmutablecompositiontrack *trackaudio = [composition addmutabletrackwithmediatype:avmediatypeaudio preferredtrackid:kcmpersistenttrackid_invalid];  // your_duration cmtimesubstruct(asset.duration, yourtime_start); [trackvideo inserttimerange:cmtimerangemake(yourtime_start, your_duration)                     oftrack:assettrackvideo                      attime:kcmtimezero                       error:nil];  [trackaudio inserttimerange:cmtimerangemake(yourtime_start, your_duration)                     oftrack:assettrackaudio                      attime:kcmtimezero                       error:nil];  // orientation change if needed  nsstring* filename = [nsstring stringwithformat:@"videofilename-%d.mov",arc4random() % 1000]; nsstring* path = [nstemporarydirectory() stringbyappendingpathcomponent:filename];  nsurl *exporterurl = [nsurl fileurlwithpath:path];  // create exporter avassetexportsession *exporter = [[avassetexportsession alloc] initwithasset:composition presetname:avassetexportpresethighestquality]; exporter.outputurl = exporterurl; exporter.outputfiletype = avfiletypequicktimemovie; exporter.shouldoptimizefornetworkuse = yes;  [exporter exportasynchronouslywithcompletionhandler:^{          // nslog(@"finished output composition error '%@' reason '%@'",   exporter.error.localizeddescription,exporter.error.localizedfailurereason);     }];