iphone - Taking thumbnail image from video always returns null -

i trying first thumbnail video.

i tried following:

one

avurlasset *asset = [[avurlasset alloc] initwithurl:[nsurl fileurlwithpath:_moviepath] options:nil]; avassetimagegenerator *gen = [[avassetimagegenerator alloc] initwithasset:asset]; gen.appliespreferredtracktransform = yes; cmtime time = cmtimemakewithseconds(0.0, 600); nserror *error = nil; cmtime actualtime;  cgimageref image = [gen copycgimageattime:time actualtime:&actualtime error:&error]; uiimage *thumb = [[uiimage alloc] initwithcgimage:image]; cgimagerelease(image); nslog(@"the error %@: image %@: url %@: ",error,_mainthumbnail,[nsurl fileurlwithpath:_moviepath] ); 

however, log is:

the error (null): image (null):  url file:///private/var/mobile/applications/d1293bdc-ea7e-4ac7-ad3c-1ba3548f37d6/tmp/trim.6f0c4631-e5e8-43cd-bf32-9b8f09d4acf1.mov:  

two

avurlasset *asset=[[avurlasset alloc] initwithurl:[nsurl fileurlwithpath:_moviepath] options:nil];     avassetimagegenerator *generator = [[avassetimagegenerator alloc] initwithasset:asset];     generator.appliespreferredtracktransform=true;      cmtime thumbtime = cmtimemakewithseconds(0,30);      avassetimagegeneratorcompletionhandler handler = ^(cmtime requestedtime, cgimageref im, cmtime actualtime, avassetimagegeneratorresult result, nserror *error){         if (result != avassetimagegeneratorsucceeded) {             nslog(@"couldn't generate thumbnail, error:%@", error);         }         _mainthumbnail.image = [uiimage imagewithcgimage:im];         nslog(@"thumbnails %@ ",_mainthumbnail.image);     };      cgsize maxsize = cgsizemake(320, 180);     generator.maximumsize = maxsize;     [generator generatecgimagesasynchronouslyfortimes:[nsarray arraywithobject:[nsvalue valuewithcmtime:thumbtime]] completionhandler:handler]; 

the log thumnails null.

why image null? looked in other forums, , suggested use fileurlwithpath -which using.

i using ios7

you can try method. takes first frame of video @ given url , returns uiimage.

- (uiimage *)thumbnailfromvideoaturl:(nsurl *)url {     avasset *asset = [avasset assetwithurl:url];      //  thumbnail @ start of video     cmtime thumbnailtime = [asset duration];     thumbnailtime.value = 0;      //  image video @ given time     avassetimagegenerator *imagegenerator = [[avassetimagegenerator alloc] initwithasset:asset];      cgimageref imageref = [imagegenerator copycgimageattime:thumbnailtime actualtime:null error:null];     uiimage *thumbnail = [uiimage imagewithcgimage:imageref];     cgimagerelease(imageref);      return thumbnail; } 

the method not check errors code using ok nil returned if fails.

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edit: clarification of cmtime values

cmtime has

• timescale - think fps (frames per second) of video (25 fps -> 1s of video has 25 video frames)
• value - identification of concrete frame. in code above, says frame want take thumbnail of.

for calculation of frame @ exact time, have make calculation:

value = timescale * seconds_to_skip 

which equivalent to

"frame of video take" = "fps" * "number of seconds skip" 

if want take example 1st frame of 2nd second of video, want in fact skip 1st second of video. use:

cmtime thumbnailtime = [asset duration]; thumbnailtime.value = thumbnailtime.timescale * 1; 

another look: want skip first 1s of video , take thumbnail. i.e. on 25 fps, want skip 25 frames. cmtime.value = 25 (skip 25 frames).