Need hints for using iPhone SDK's AVMutableVideoComposition

Question

The AVFoundation framework provides the AVMutableVideoComposition class (the mutable variant of AVVideoComposition). It looks like you can render 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, really. The following code called from a UIViewController appears to work to create the composition and the animation but, then, well, I'm stumped as to how to work with the composition. Any help or guidance is greatly 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's 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, Jon

Answer 1

Not sure if it helps.

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