how to control orientation of video assembled with AVMutableComposition

Question

I am assembling a bunch of video clips filmed on the iPhone in portrait mode. To assemble them I am taking straightforward approach as follows:

AVURLAsset to get hold

Answer 1

If all you want is preserve you video orientation you may want to assign AVMutableCompositionTrack prefferedTransition value from AVAssetTrack like this:

AVAssetTrack *videoAssetTrack= [[videoAsset tracksWithMediaType:AVMediaTypeVideo] lastObject];

AVMutableCompositionTrack *videoCompositionTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[videoCompositionTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration) ofTrack:videoAssetTrack atTime:kCMTimeZero error:&error];

videoCompositionTrack.preferredTransform = videoAssetTrack.preferredTransform;