Rotate video not woking as expect - swift

Question

I had function to rotate video, first time I rotate with angle = pi / 2 it working normal, but if I continue rotate it with (pi / 2), it not working, it still only rotate (pi / 2), but I expect it rotate pi. Any one can help me, thanks
let rotateTransform = CGAffineTransform(rotationAngle: CGFloat((self.rotateAngle * Double.pi)/180))
let videoAsset = AVURLAsset(url: sourceURL)
let mixComposition = AVMutableComposition()
let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
var clipVideoTrack = videoAsset.tracks(withMediaType: .video)
try? compositionVideoTrack?.insertTimeRange(CMTimeRange(start: .zero, duration: videoAsset.duration), of: clipVideoTrack[0], at: .zero)
compositionVideoTrack?.preferredTransform = videoAsset.preferredTransform
let videoTrack = videoAsset.tracks(withMediaType: .video)[0]
let videoSize = videoTrack.naturalSize
let videoComposition = AVMutableVideoComposition()
videoComposition.renderSize = videoSize
let timeScale = CMTimeScale(videoTrack.nominalFrameRate)
videoComposition.frameDuration = CMTime(value: 1, timescale: timeScale)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(start: .zero, duration: mixComposition.duration)
let mixVideoTrack = mixComposition.tracks(withMediaType: .video)[0]
mixVideoTrack.preferredTransform = rotateTransform
let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: mixVideoTrack)
layerInstruction.setTransform(mixVideoTrack.preferredTransform, at: .zero)
instruction.layerInstructions = [layerInstruction]
videoComposition.instructions = [instruction]
guard let exportSession = AVAssetExportSession(asset: mixComposition,
presetName: AVAssetExportPresetPassthrough) else {
return
}
exportSession.outputURL = outputURL
exportSession.outputFileType = .mov
exportSession.videoComposition = videoComposition
exportSession.exportAsynchronously { [weak self] in
self?.handleExportSession(exportSession: exportSession, sourceURL: sourceURL, outputURL: outputURL)
}
}

Answer 1

If you set the transform, this will always be applied to the original orientation. So when you set a rotation matrix by pi/2, the original will be rotated by pi/2. If you apply the same rotation matrix again, the original will be rotated again by pi/2. What you need is to combine the current transform with the new rotation and then set that resulting transformation.
Something like:
let currentTransform = mixVideoTrack.preferredTransform // or whereever you get it from
let newTransform = currentTransform.rotated(by: CGFloat((self.rotateAngle * Double.pi)/180))
mixVideoTrack.preferredTransform = newTransform