Need Tips for Using iPhone SDK AVMutableVideoComposition

Question

The AVFoundation structure provides the AVMutableVideoComposition class (a mutable version of AVVideoComposition). It looks like you can visualize CoreAnimations directly to an instance of this class to create a video, but I don’t know how to save the composition to a file or how to work with it at all. The following code, called from the UIViewController, seems to work for composition and animation, but, well, I don’t understand how to work with the composition. Any help or guidance is appreciated.

static AVMutableVideoComposition *videoComposition = nil;
- (void)animationDidStop:(CAAnimation *)animation finished:(BOOL)flag {
 //Do something with videoComposition here... how to save it to a file?
 NSLog(@"videoComposition: %@", videoComposition);
 [videoComposition release]; videoComposition = nil;
}

- (IBAction)createVideoComposition:(id)sender {
 AVVideoCompositionCoreAnimationTool *videoCompositionCoreAnimationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:self.view.layer inLayer:self.view.layer];
 videoComposition = [[AVMutableVideoComposition videoComposition] retain];
 [videoComposition setRenderSize:CGSizeMake(320.0, 480.0)];
 [videoComposition setRenderScale:1.0];
 [videoComposition setFrameDuration:CMTimeMake(1, 10)];
 [videoComposition setAnimationTool:videoCompositionCoreAnimationTool];
 //add a basic animation to shake the controller view
 CAKeyframeAnimation *shakeAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
 shakeAnimation.delegate = self;
 shakeAnimation.removedOnCompletion = YES;
 shakeAnimation.duration = 0.5;
 CGMutablePathRef path = CGPathCreateMutable();
 CGFloat midX = self.view.center.x;
 CGFloat midY = self.view.center.y;
 CGPathMoveToPoint(path, nil, midX, midY);
 CGPathAddLineToPoint(path, nil, midX + 10.0, midY);
 CGPathAddLineToPoint(path, nil, midX - 20.0, midY);
 CGPathAddLineToPoint(path, nil, midX + 15.0, midY);
 CGPathAddLineToPoint(path, nil, midX - 5.0, midY);
 CGPathAddLineToPoint(path, nil, midX, midY);
 shakeAnimation.path = path;
 CFRelease(path);
 [self.view.layer addAnimation:shakeAnimation forKey:@"shakeAnimation"];
}

Thanks, John

Answer 1

Not sure if this helps.

    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetHighestQuality];
    session.videoComposition = videoComposition;
    session.outputURL = outputURL;
    session.outputFileType = AVFileTypeQuickTimeMovie;
    [session exportAsynchronouslyWithCompletionHandler:
         ^(void )
{
        NSLog(@"TADA!")
    }];