AVAssetExportSession ignoring videoComposition rotation & stripping metadata - ios

Question

I am attempting to rotate video prior to upload on my iOS device because other platforms (such as android) do not properly interpret the rotation information in iOS-recorded videos and, as a result, play them improperly rotated.
I have looked at the following stack posts but have not had success apply any of them to my case:
iOS rotate every frame of video
Rotating Video w/ AVMutableVideoCompositionLayerInstruction
AVMutableVideoComposition rotated video captured in portrait mode
iOS AVFoundation: Setting Orientation of Video
I coped the Apple AVSimpleEditor project sample, but unfortunately all that ever happens is, upon creating an AVAssetExportSession and calling exportAsynchronouslyWithCompletionHandler, no rotation is performed, and what's worse, rotation metadata is stripped out of the resulting file.
Here is the code that runs the export:
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:[_mutableComposition copy] presetName:AVAssetExportPresetPassthrough];
exportSession.outputURL = outputURL;
exportSession.outputFileType = AVFileType3GPP;
exportSession.shouldOptimizeForNetworkUse = YES;
exportSession.videoComposition = _mutableVideoComposition;
[exportSession exportAsynchronouslyWithCompletionHandler:^(void)
{
NSLog(#"Status is %d %#", exportSession.status, exportSession.error);
handler(exportSession);
[exportSession release];
}];
The values _mutableComposition and _mutableVideoComposition are initialized by this method here:
- (void) getVideoComposition:(AVAsset*)asset
{
AVMutableComposition *mutableComposition = nil;
AVMutableVideoComposition *mutableVideoComposition = nil;
AVMutableVideoCompositionInstruction *instruction = nil;
AVMutableVideoCompositionLayerInstruction *layerInstruction = nil;
CGAffineTransform t1;
CGAffineTransform t2;
AVAssetTrack *assetVideoTrack = nil;
AVAssetTrack *assetAudioTrack = nil;
// Check if the asset contains video and audio tracks
if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {
assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];
}
if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {
assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];
}
CMTime insertionPoint = kCMTimeZero;
NSError *error = nil;
// Step 1
// Create a composition with the given asset and insert audio and video tracks into it from the asset
// Check whether a composition has already been created, i.e, some other tool has already been applied
// Create a new composition
mutableComposition = [AVMutableComposition composition];
// Insert the video and audio tracks from AVAsset
if (assetVideoTrack != nil) {
AVMutableCompositionTrack *compositionVideoTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetVideoTrack atTime:insertionPoint error:&error];
}
if (assetAudioTrack != nil) {
AVMutableCompositionTrack *compositionAudioTrack = [mutableComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, [asset duration]) ofTrack:assetAudioTrack atTime:insertionPoint error:&error];
}
// Step 2
// Translate the composition to compensate the movement caused by rotation (since rotation would cause it to move out of frame)
t1 = CGAffineTransformMakeTranslation(assetVideoTrack.naturalSize.height, 0.0);
// Rotate transformation
t2 = CGAffineTransformRotate(t1, degreesToRadians(90.0));
// Step 3
// Set the appropriate render sizes and rotational transforms
// Create a new video composition
mutableVideoComposition = [AVMutableVideoComposition videoComposition];
mutableVideoComposition.renderSize = CGSizeMake(assetVideoTrack.naturalSize.height,assetVideoTrack.naturalSize.width);
mutableVideoComposition.frameDuration = CMTimeMake(1, 30);
// The rotate transform is set on a layer instruction
instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [mutableComposition duration]);
layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:(mutableComposition.tracks)[0]];
[layerInstruction setTransform:t2 atTime:kCMTimeZero];
// Step 4
// Add the transform instructions to the video composition
instruction.layerInstructions = #[layerInstruction];
mutableVideoComposition.instructions = #[instruction];
TT_RELEASE_SAFELY(_mutableComposition);
_mutableComposition = [mutableComposition retain];
TT_RELEASE_SAFELY(_mutableVideoComposition);
_mutableVideoComposition = [mutableVideoComposition retain];
}
I pulled this method from AVSERotateCommand from here. Can anyone suggest why this method would not successfully rotate my video by the necessary 90 degrees?

Answer 1

because you are using AVAssetExportPresetPassthrough the AVAssetExportSession will ignore the videoComposition, use any other preset.