objective c - CGImageDestinationFinalize save large gif the image become blur -

i want create gif asset, in osx10.12 right. in osx10.11, when record large image 5120 * 2880, , framecount larger 10, final gif become blur, , place white.

the cgimage asset right, after cgimagedestinationaddimage gif got wrong. guess maybe reason image large compress , memory cann't afford?

hope can help, help.

- (void)animatedgiffromvideoasset:(avasset *)asset                     timerange:(cmtimerange)timerange                 timeincrement:(float)increment                      destsize:(cgsize)destsize                      progress:(void(^)(float progress))convertprogress                    completion:(giffrommoviecompletion)completion { @autoreleasepool {      dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default, 0), ^{         avassetimagegenerator * generator = [avassetimagegenerator assetimagegeneratorwithasset:asset];          float movielength = (float)timerange.duration.value / timerange.duration.timescale;         int framecount = movielength / increment;         float tolerance = 0.01f;          nsstring *tempfile = [nstemporarydirectory() stringbyappendingpathcomponent:@"temp.gif"];         cfurlref fileurl = (__bridge cfurlref)[nsurl fileurlwithpath:tempfile];          cgimagedestinationref destination = cgimagedestinationcreatewithurl(fileurl, kuttypegif, framecount, nil);          generator.requestedtimetolerancebefore = cmtimemakewithseconds(tolerance, 600);         generator.requestedtimetoleranceafter = cmtimemakewithseconds(tolerance, 600);         generator.appliespreferredtracktransform = yes;          nsdictionary *frameproperties = [nsdictionary dictionarywithobject:[nsdictionary dictionarywithobject:[nsnumber numberwithfloat:increment] forkey:(nsstring *)kcgimagepropertygifdelaytime] forkey:(nsstring *)kcgimagepropertygifdictionary];         nsdictionary *gifproperties = [nsdictionary dictionarywithobject:[nsdictionary dictionarywithobject:[nsnumber numberwithint:0] forkey:(nsstring *)kcgimagepropertygifloopcount] forkey:(nsstring *)kcgimagepropertygifdictionary];          cgimagedestinationsetproperties(destination, (cfdictionaryref)gifproperties);          // 压缩gif靠限制转换的最大gif宽度         if (!cgsizeequaltosize(nszerosize, destsize)) {             generator.maximumsize = destsize;         }          nserror * error = nil;         float beginseconds = cmtimegetseconds(timerange.start);          (int = 0; < framecount; ++) {              float progress = (i + 1) * 1.0f / framecount;             convertprogress(progress);              cmtime imagetime = cmtimemakewithseconds(beginseconds + * increment, 600);             cgimageref image = [generator copycgimageattime:imagetime actualtime:null error:&error];             if (error) {                 if (destination) {                     cfrelease(destination);                     destination = null;                 }                  completion(nil, error);                 return;             }             cgimagedestinationaddimage(destination, image, (cfdictionaryref)frameproperties);              if (image) {                 cfrelease(image);                 image = null;             }              usleep(10);          }         cgimagedestinationfinalize(destination);          if (destination) {             cfrelease(destination);             destination = null;         }          nsdata *gifdata = [nsdata datawithcontentsoffile:tempfile];          completion(gifdata, error);     }); } 

}