iOS 4.3 crashes when uploading video - objective-c

Question

I have an iPhone app that uploads images and video to a web service using ASIHTTPRequest. Everything works great on devices running iOS 5, but crashes on 4.3 and below devices after returning from the UIImagePickerController. The video is compressed bu=y the picker, then the app crashes. Below is the code from the -(void)imagePickerController: didFinishPickingMediaWithInfo: method, and also from the method that post the video to the server and a method that captures an image from the video to use as a thumbnail. Any ideas on what's causing the crashes in 4.3?
-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
self.mediaType = [info objectForKey:UIImagePickerControllerMediaType];
if ([self.mediaType isEqualToString:(NSString *)kUTTypeMovie])
{
NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL];
// Get asset to use for orientation determination
AVAsset *myAsset = [AVAsset assetWithURL:videoURL];
self.videoOrientation = [self UIInterfaceOrientationToString:[self orientationForTrack:myAsset]];
UIImage *videoThumbnail = [self getVideoThumbnailFromAVAsset:myAsset];
self.photoImageView.image = videoThumbnail;
self.videoData = [[NSMutableData alloc]initWithContentsOfURL:videoURL];
}
[self dismissModalViewControllerAnimated:YES];
}
-(UIImage*)getVideoThumbnailFromAVAsset:(AVAsset *)myAsset {
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:myAsset];
Float64 durationSeconds = CMTimeGetSeconds([myAsset duration]);
CMTime midpoint = CMTimeMakeWithSeconds(durationSeconds/2.0, 600);
NSError *error = nil;
CMTime actualTime;
UIImage *myImage;
CGImageRef halfWayImage = [imageGenerator copyCGImageAtTime:midpoint actualTime:&actualTime error:&error];
if (halfWayImage != NULL) {
myImage = [UIImage imageWithCGImage:halfWayImage];
CGImageRelease(halfWayImage);
}
return myImage;
}
- (void)postMessage:(id)sender {
self.uploadButton.enabled = NO;
[self.descriptionTextField resignFirstResponder];
[self.titleTextField resignFirstResponder];
NSUserDefaults *settings = [NSUserDefaults standardUserDefaults];
NSString *sessionKey = [settings stringForKey: #"sessionKey"];
// build URL for request
NSString *baseURL;
NSString *endPoint;
// code here that creates the url component strings baseURL and endPoint
NSString *fullURL = [NSString stringWithFormat:#"%#%#", baseURL, endPoint];
NSURL *url = [NSURL URLWithString:fullURL];
ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
request.postFormat = ASIMultipartFormDataPostFormat;
NSString *teamIDStr = [NSString stringWithFormat:#"%d",[self.teamID intValue]];
[request setPostValue:sessionKey forKey:#"sessionKey"];
[request setPostValue:teamIDStr forKey:#"TeamID"];
[request setPostValue:titleTextField.text forKey:#"lessonName"];
[request setPostValue:descriptionTextField.text forKey:#"lessonDesc"];
[request setPostValue:self.videoOrientation forKey:#"videoOrientation"];
//create video file name
NSDate *date1=[NSDate date];
NSDateFormatter *formatter1 = [[NSDateFormatter alloc] init];
[formatter1 setDateFormat:#"hhmm"];
NSString *valuestr = [formatter1 stringFromDate:date1];
NSString *moviename = [NSString stringWithFormat:#"video_%#.mov", valuestr];
[request setData:self.videoData withFileName:moviename andContentType:#"video/quicktime" forKey:#"file1.mov"];
[request setUploadProgressDelegate:self.progressBar];
[request setShowAccurateProgress:YES];
self.progressBar.hidden = NO;
[request setDelegate:self];
[request setTimeOutSeconds:600];
[request startAsynchronous];
}

Answer 1

SImple answer to this issue: The AVAsset class method
+ (id)assetWithURL:(NSURL *)URL
is not available before iOS 5.0. You must use the concrete subclass AVURLAsset to instantiate an AVAsset for iOS 4.0 and 4.3, using its class method
+ (AVURLAsset *)URLAssetWithURL:(NSURL *)URL options:(NSDictionary *)options