Getting thumbnail of a video picked from photos library - ios

Question

I know this question has been asked many times on stackoverflow. But my problem is different.
I am iterating on the albumns of photos library to get all videos and their thumbnails.
Now, the problem is, my code is very slow to get the thumbnail of each video. For example, there is 14 videos in my camera roll and the total time taken to generate the thumbnail is around 3-4 seconds. I am using this code.
+(UIImage*)imageFromVideoAtURL:(NSURL*)contentURL {
UIImage* theImage = nil;
AVURLAsset* asset = [[AVURLAsset alloc] initWithURL:contentURL options:nil];
AVAssetImageGenerator* generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
generator.appliesPreferredTrackTransform = YES;
NSError* err = NULL;
CMTime time = CMTimeMake(1, 60);
CGImageRef imgRef = [generator copyCGImageAtTime:time actualTime:NULL error:&err];
theImage = [[[UIImage alloc] initWithCGImage:imgRef] autorelease];
CGImageRelease(imgRef);
[asset release];
[generator release];
return theImage;
}
I am finding a way to get the thumbnail of all videos very fast so that user has not to wait. I have seen apps on Apple store that are doing the same thing in just micro seconds. Please help.
I have also tried this code to generate the thumbnail, it is also very slow.
MPMoviePlayerController *moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:mediaUrl];
moviePlayer.shouldAutoplay = NO;
UIImage *thumbnail = [[moviePlayer thumbnailImageAtTime:0.0 timeOption:MPMovieTimeOptionNearestKeyFrame] retain];
[imageView setImage:thumbnail]; //imageView is a UIImageView

Answer 1

If you are loading videos from image library, it should already have the embedded thumbnail of the video. This can be accessed using thumbnail or aspectRatioThumnail methods of ALAsset class.
So in your case the thumbnails could be loaded like:
ALAssetLibrary* lib = [ALAssetLibrary new];
[lib assetForURL:contentURL resultBlock:^(ALAsset* asset) {
CGImageRef thumb = [asset thumbnail];
dispatch_async(dispatch_get_main_queue(), ^{
//do any UI operation here with thumb
});
}];
Please make sure to make any UIKit call in the main queue as assetForURL:: method may invoke the resultBlock in some background thread.