ios - Why don't I get video when exporting a movie using AVAssetExportSession? -

it trimming audio, video blank.

this function initiates trimming

- (void)viewdidload {     [super viewdidload];     // additional setup after loading view.     self.view.backgroundcolor = [uicolor blackcolor];      [[nsnotificationcenter defaultcenter] addobserver:self                                          selector:@selector(finishedtrimming:)                                              name:@"videofinishedtrimming"                                            object:nil];     nsurl *furl = [nsurl fileurlwithpath:[nstemporarydirectory() stringbyappendingpathcomponent:@"capture0.mp4"]];      //[self playvideowithurl:furl]; //play original video      //play trimmed video     cmtime starttrim = cmtimemake(0, 1);     cmtime endtrim = cmtimemake(2,1);     cmtimerange exporttimerange = cmtimerangefromtimetotime(starttrim, endtrim);      [processinghelper trimassetwithurl:furl andrange:exporttimerange]; } 

this function exports , trims video.

+(void)trimassetwithurl:(nsurl *)urlin andrange:(cmtimerange)timerangein {     avasset *videoasset = [avasset assetwithurl:urlin];      //creates session videoasset     avassetexportsession *exportsession = [[avassetexportsession alloc] initwithasset:videoasset presetname:avassetexportpresethighestquality];      //creates path export  - saving temporary directory     nsstring* filename = [nsstring stringwithformat:@"trimmedcapture%d.mp4", 0];     nsstring* path = [nstemporarydirectory() stringbyappendingpathcomponent:filename];      //checks if there file @ output url.  session not overwrite previous data     if ([[nsfilemanager defaultmanager] fileexistsatpath:path])     {         nslog(@"removing item @ path: %@", path);         [[nsfilemanager defaultmanager] removeitematpath:path error:nil];     }      //set output url     exportsession.outputurl = [nsurl fileurlwithpath:path];      //set output file type     exportsession.outputfiletype = avfiletypempeg4; //avfiletypeac3; // avfiletypempeglayer3; // avfiletypewave; // avfiletypequicktimemovie;      exportsession.timerange = timerangein;      exportsession.metadata = nil;      //exports!     [exportsession exportasynchronouslywithcompletionhandler:^{         switch (exportsession.status) {             case avassetexportsessionstatuscompleted:{                 nslog(@"export complete");                 nsdictionary *options = [nsdictionary dictionarywithobjectsandkeys:exportsession.outputurl, @"outputurl", nil];                 [[nsnotificationcenter defaultcenter] postnotificationname:@"videofinishedtrimming" object:self userinfo:options];                 break;             }             case avassetexportsessionstatusfailed:                 nslog(@"export error: %@", [exportsession.error description]);                 break;             case avassetexportsessionstatuscancelled:                 nslog(@"export cancelled");                 break;             default:                 break;         }     }];     exportsession = nil; } 

this function initiates playing of video

-(void)finishedtrimming:(nsnotification *)notification {     nsdictionary *userinfo = notification.userinfo;     nsurl *outputurl = [userinfo objectforkey:@"outputurl"];     [self playvideowithurl:outputurl];  } 

this function plays video

-(void)playvideowithurl:(nsurl *)furl {     nsdata *moviedata;     nserror *datareadingerror = nil;     moviedata = [nsdata datawithcontentsofurl: furl options:nsdatareadingmapped error:&datareadingerror];     if(moviedata != nil)         nslog(@"successfully loaded data.");     else         nslog(@"failed load data error = %@", datareadingerror);       //avplayer     self.avplayer = [avplayer playerwithurl:furl];     avplayerlayer *avplayerlayer = [avplayerlayer playerlayerwithplayer:self.avplayer];     avplayerlayer.frame = self.vplaybackmovie.bounds;     avplayerlayer.videogravity = avlayervideogravityresizeaspectfill;     avplayerlayer.needsdisplayonboundschange = yes;      [self.vplaybackmovie.layer addsublayer:avplayerlayer];     self.vplaybackmovie.layer.needsdisplayonboundschange = yes;     [self.avplayer play]; } 

thanks chrish, right! export taking place on thread in handler need main queue...

i needed main thread after

case avassetexportsessionstatuscompleted:{     dispatch_async(dispatch_get_main_queue(), ^{         //post notification!     });     break; }