AVFoundation framework takes delay to create thumbnails - iphone

Question

I am using AVFoundation framework in my iPad app to record videos.When recording of a video is completed, I create a thumbnail image for same video using AVFoundation.But if I record two videos without much time delay in between then thumbnail is not created properly.Clearly it's taking some delay.How to avoid that or at least how can I know when the thumbnail of previous video has got created completely so that I can show some 'Wait' symbol to the user for that time period?
Please help as I am having no clue to resolve the issue.
//delegate method which gets called when recording ends.
//Here I create the thumb and store it in self.thumb
-(void)recorder:(AVCamRecorder *)recorder recordingDidFinishToOutputFileURL:(NSURL *)outputFileURL error:(NSError *)error
{
self.thumb=nil;
AVURLAsset *asset=[[AVURLAsset alloc] initWithURL:outputFileURL options:nil];
AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
generator.appliesPreferredTrackTransform=TRUE;
[asset release];
CMTime thumbTime = CMTimeMakeWithSeconds(0,1);
AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
if (result != AVAssetImageGeneratorSucceeded) {
NSLog(#"couldn't generate thumbnail, error:%#", error);
}
self.thumb=[UIImage imageWithCGImage:im];
[generator release];
};
CGSize maxSize = CGSizeMake(320, 180);
generator.maximumSize = maxSize;
[generator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:thumbTime]] completionHandler:handler];
if ([[UIDevice currentDevice] isMultitaskingSupported]) {
[[UIApplication sharedApplication] endBackgroundTask:[self backgroundRecordingID]];
}
if ([[self delegate] respondsToSelector:#selector(captureManagerRecordingFinished:)]) {
[[self delegate] captureManagerRecordingFinished:self];
}
}
[self copyFileToDocuments:outputFileURL];
}
//Save video and thumbnail to documents
- (void) copyFileToDocuments:(NSURL *)fileURL
{
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd_HH-mm-ss"];
NSString *destinationPath = [documentsDirectory stringByAppendingFormat:#"/output_%#.mov", [dateFormatter stringFromDate:[NSDate date]]];
[dateFormatter release];
NSError *error;
if (![[NSFileManager defaultManager] copyItemAtURL:fileURL toURL:[NSURL fileURLWithPath:destinationPath] error:&error]) {
if ([[self delegate] respondsToSelector:#selector(captureManager:didFailWithError:)]) {
[[self delegate] captureManager:self didFailWithError:error];
}
}
else
{
destinationPath=[[destinationPath lastPathComponent]stringByDeletingPathExtension];
[self saveImage:self.thumb withName:destinationPath];
}
}
//Method Where I save self.thumb in app documents
-(void) saveImage:(UIImage*)image withName:(NSString*)fileName
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
//Save Image
NSData *imageData = UIImagePNGRepresentation(image); //convert image into .png format.
NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"%#.png",fileName]];
[fileManager createFileAtPath:fullPath contents:imageData attributes:nil];
}
Above is my code.
But self.thumb is not getting properly saved if I don't give delay in two recordings.

Answer 1

I used a different method.When user clicks 'Record' I first click a photo from camera and then start recording the video.Later I use the same photo as a thumbnail.
I know this is not the best approach but the best thing is its working ;)
Hope this helps someone with the same problem.