How to set preferredTransform to exported video with AVAssetExportSession - objective-c

Question

I am trying to export a video with the same rotation transform that camera does. For example, I film some video with1920x1080 resolution(landscape) with a CGAffineTransform(0, -1, 1, 0, 1080, 0). After some work I want to export that video with the same naturalSize and preferredTransform that the original video, but the ExportSession is rotating my video.
The code below transform the original video to portrait mode with a portrait rotation, but that is not what I want to achieve.
Any idea? Thanks in advance.
- (void)applyDrawWithCompletion:(void(^)(NSURL *))completion {
//setup video asset layer
AVURLAsset* videoAsset = (AVURLAsset *)self.avPlayer.currentItem.asset;
AVMutableComposition* mixComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *compositionVideoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *clipVideoTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
ofTrack:clipVideoTrack
atTime:kCMTimeZero error:nil];
AVMutableCompositionTrack *compositionAudioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
AVAssetTrack *clipAudioTrack = [videoAsset tracksWithMediaType:AVMediaTypeAudio][0];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [mixComposition duration]) ofTrack:clipAudioTrack atTime:kCMTimeZero error:nil];
[compositionVideoTrack setPreferredTransform:clipVideoTrack.preferredTransform];
//new layer with draw image
CGSize videoSize = CGSizeMake(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.width);
CALayer *drawLayer = [CALayer layer];
drawLayer.contents = (id)self.tempDrawImage.image.CGImage;
drawLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
//proper sorting of video layers
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:drawLayer];
AVMutableVideoComposition* videoComp = [AVMutableVideoComposition videoComposition];
videoComp.renderSize = videoSize;
videoComp.frameDuration = CMTimeMake(1, 30);
videoComp.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
//Adding layer along asset duration
AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mixComposition duration]);
AVAssetTrack *videoTrack = [[mixComposition tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
AVMutableVideoCompositionLayerInstruction* layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
//Apply transform to layer instructions
[layerInstruction setTransform:clipVideoTrack.preferredTransform atTime:kCMTimeZero];
instruction.layerInstructions = [NSArray arrayWithObject:layerInstruction];
videoComp.instructions = [NSArray arrayWithObject: instruction];
//Export edited video
AVAssetExportSession *assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];
assetExport.videoComposition = videoComp;
NSString *exportPath = [NSTemporaryDirectory() stringByAppendingPathComponent:#"editedVideo.mov"];;
if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) {
[[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}
assetExport.outputFileType = AVFileTypeQuickTimeMovie;
assetExport.outputURL = [NSURL fileURLWithPath:exportPath];
assetExport.shouldOptimizeForNetworkUse = YES;
[assetExport exportAsynchronouslyWithCompletionHandler:^(void) {
if (assetExport.status == AVAssetExportSessionStatusCompleted) {
completion(assetExport.outputURL);
}else if(assetExport.status == AVAssetExportSessionStatusFailed || assetExport.status == AVAssetExportSessionStatusCancelled){
completion(nil);
}
}];
}

Answer 1

I processed the original camera video with the same method and add the following code:
CGAffineTransform t = clipVideoTrack.preferredTransform;
BOOL isPortrait = (t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0) || (t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0);
//new layer with draw image
CGSize videoSize = clipVideoTrack.naturalSize;
if (isPortrait) {
videoSize = CGSizeMake(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.width);
}
This changed the landscape video to portrait with the same transform that other edited and processed videos.
This is not what I was looking for, but it solve my problem. If someone know how to achieve the original question goal please feel free to add an answer.