AVMutableComposition Rotates Videos

Question

I've recently discovered an issue using AVMutableComposition and I'm looking for some insight into this.

I want to be able to record video in two orientations - landscape left and right. When I record videos in landscape right (home button is on the right), they are added to the composition and played in the correct orientation. However, if I record it in orientation left (home button on the left), these clips are played upside down.

BUT, they are only played upside-down if they are inserted into the composition. Otherwise they play in the correct orientation. Why is the composition reversing the rotation of clips shot in landscape left? How can I fix this? Any help is appreciated!

Answer 1

Here's a slightly easier way if you simply want to maintain original rotation.

// Grab the source track from AVURLAsset for example.
AVAssetTrack *assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo].lastObject;

// Grab the composition video track from AVMutableComposition you already made.
AVMutableCompositionTrack *compositionVideoTrack = [composition tracksWithMediaType:AVMediaTypeVideo].lastObject;

// Apply the original transform.    
if (assetVideoTrack && compositionVideoTrack) {
   [compositionVideoTrack setPreferredTransform:assetVideoTrack.preferredTransform];
}

// Export...

Answer 2

Solved my problem. Was finally able to rotate the track and translate it into the frame. Works like a charm.

    //setting up the first video based on previous recording
    CMTimeRange videoDuration = CMTimeRangeMake(kCMTimeZero, [self.previousRecording duration]);
    AVAssetTrack *clipVideoTrack = [[self.previousRecording tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    AVAssetTrack *clipAudioTrack = [[self.previousRecording tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
    [compositionVideoTrack insertTimeRange:videoDuration ofTrack:clipVideoTrack atTime:nextClipStartTime error:nil];
    [compositionAudioTrack insertTimeRange:videoDuration ofTrack:clipAudioTrack atTime:nextClipStartTime error:nil];

    //our first track instruction - set up the instruction layer, then check the orientation of the track
    //if the track is in landscape-left mode, it needs to be rotated 180 degrees (PI)
    AVMutableVideoCompositionLayerInstruction *firstTrackInstruction =
         [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];

    if([self orientationForTrack:clipVideoTrack] == UIDeviceOrientationLandscapeLeft) {
        CGAffineTransform rotation = CGAffineTransformMakeRotation(M_PI);
        CGAffineTransform translateToCenter = CGAffineTransformMakeTranslation(640, 480);
        CGAffineTransform mixedTransform = CGAffineTransformConcat(rotation, translateToCenter);
        [firstTrackInstruction setTransform:mixedTransform atTime:kCMTimeZero];
    }