How to flip a video using AVFoundation - ios

Question

I've recorded a video with the front facing camera and the output is mirrored...
I've tried using AVMutablecomposition and layerinstructions to flip the video but no luck.
Googling and searching Stack Overflow has been fruitless so I bet a simple, straight forward example of how to do this is something that would benefit many.

Answer 1

Theres no indication on what you are using to record the video, ill assume AVCaptureSession + AVCaptureVideoDataOutput
lazy var videoFileOutput: AVCaptureVideoDataOutput = AVCaptureVideoDataOutput()
let v = videoFileOutput.connectionWithMediaType(AVMediaTypeVideo)
v.videoOrientation = .Portrait
v.videoMirrored = true

Answer 2

You can use -[AVMutableVideoCompositionLayerInstruction setTransform:atTime:]
CGAffineTransform transform = CGAffineTransformMakeTranslation(self.config.videoSize, 0);
transform = CGAffineTransformScale(transform, -1.0, 1.0);
[videoCompositionLayerInstruction setTransform:transform atTime:videoTime];
// then append video tracks
// [compositionTrack insertTimeRange:timeRange ofTrack:track atTime:atTime error:&error];
// apply instructions
videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, composition.duration);
videoCompositionInstruction.layerInstructions = #[videoCompositionLayerInstruction];
videoComposition = [AVMutableVideoComposition videoComposition];
videoComposition.renderSize = CGSizeMake(self.config.videoSize, self.config.videoSize);
videoComposition.frameDuration = CMTimeMake(1, self.config.videoFrameRate);
videoComposition.instructions = #[videoCompositionInstruction];
https://github.com/ElfSundae/AVDemo/tree/ef2ca437d0d8dcb3dd41c5a272c8754a29d8a936/AVSimpleEditoriOS
Export composition:
AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:composition presetName:presetName];
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.outputURL = outputURL;
exportSession.shouldOptimizeForNetworkUse = YES;
// videoComposition contains transform instructions for video tracks
exportSession.videoComposition = videoComposition;
// audioMix contains background music for audio tracks
exportSession.audioMix = audioMix;
[exportSession exportAsynchronouslyWithCompletionHandler:^{
AVAssetExportSessionStatus status = exportSession.status;
if (status != AVAssetExportSessionStatusCompleted) {
// exportSession.error
} else {
// exportSession.outputURL
}
}];

Answer 3

After you get your output transform your video
func mirrorVideo(inputURL: URL, completion: #escaping (_ outputURL : URL?) -> ())
{
let videoAsset: AVAsset = AVAsset( url: inputURL )
let clipVideoTrack = videoAsset.tracks( withMediaType: AVMediaType.video ).first! as AVAssetTrack
let composition = AVMutableComposition()
composition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: CMPersistentTrackID())
let videoComposition = AVMutableVideoComposition()
videoComposition.renderSize = CGSize(width: clipVideoTrack.naturalSize.height, height: clipVideoTrack.naturalSize.width)
videoComposition.frameDuration = CMTimeMake(1, 30)
let transformer = AVMutableVideoCompositionLayerInstruction(assetTrack: clipVideoTrack)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30))
var transform:CGAffineTransform = CGAffineTransform(scaleX: -1.0, y: 1.0)
transform = transform.translatedBy(x: -clipVideoTrack.naturalSize.width, y: 0.0)
transform = transform.rotated(by: CGFloat(Double.pi/2))
transform = transform.translatedBy(x: 0.0, y: -clipVideoTrack.naturalSize.width)
transformer.setTransform(transform, at: kCMTimeZero)
instruction.layerInstructions = [transformer]
videoComposition.instructions = [instruction]
// Export
let exportSession = AVAssetExportSession(asset: videoAsset, presetName: AVAssetExportPreset640x480)!
let fileName = UniqueIDGenerator.generate().appending(".mp4")
let filePath = documentsURL.appendingPathComponent(fileName)
let croppedOutputFileUrl = filePath
exportSession.outputURL = croppedOutputFileUrl
exportSession.outputFileType = AVFileType.mp4
exportSession.videoComposition = videoComposition
exportSession.exportAsynchronously {
if exportSession.status == .completed {
DispatchQueue.main.async(execute: {
completion(croppedOutputFileUrl)
})
return
} else if exportSession.status == .failed {
print("Export failed - \(String(describing: exportSession.error))")
}
completion(nil)
return
}
}

Answer 4

Swift 5. AVCaptureSession:
let movieFileOutput = AVCaptureMovieFileOutput()
let connection = movieFileOutput.connection(with: .video)
if connection?.isVideoMirroringSupported ?? false {
connection?.isVideoMirrored = true
}
Same for PhotoOutput.