使用 AVMutableComposition 导出镜像视频会导致调整大小问题

Posted 2023-03-08

【中文标题】使用 AVMutableComposition 导出镜像视频会导致调整大小问题

【英文标题】：Exporting a mirrored video with AVMutableComposition causes resizing issues

【发布时间】：2018-06-10 11:25:32

【问题描述】：

如果我关闭前置摄像头上的镜像，一切都会按预期工作。但是，如果我打开它，我最终导出的视频会出现严重的大小调整问题：

这是我目前管理视频镜像的方式：

       if currentDevice == frontCamera 

            if let connection = output.connections.first 
                if connection.isVideoMirroringSupported 
                    connection.automaticallyAdjustsVideoMirroring = false
                    connection.isVideoMirrored = true //if true, this bug occurs.
                
            


        else 
             //disabling photo mirroring on backCamera
            if let connection = output.connections.first 
                if connection.isVideoMirroringSupported 
                    connection.automaticallyAdjustsVideoMirroring = false
                    connection.isVideoMirrored = false
                
            
        

这就是我导出视频的方式：

  /// Create AVMutableComposition object. This object will hold the AVMutableCompositionTrack instances.

let mainMutableComposition = AVMutableComposition()
        /// Creating an empty video track
        let videoTrack = mainMutableComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)
        let videoAssetTrack = videoAsset.tracks(withMediaType: AVMediaType.video)[0]

        do 
            //Adding the video track
            try videoTrack?.insertTimeRange(CMTimeRange(start: kCMTimeZero, duration: videoAsset.duration), of: videoAsset.tracks(withMediaType: AVMediaType.video).first!, at: kCMTimeZero)

         catch 
            completion(false,  nil)
        

        /// Adding audio if user wants to.
        if withAudio 
            do 
                //Adding the video track
                let audio = videoAsset.tracks(withMediaType: AVMediaType.audio).first
                if audio != nil 
                    let audioTrack = mainMutableComposition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: kCMPersistentTrackID_Invalid)
                    try audioTrack?.insertTimeRange(CMTimeRange(start: kCMTimeZero, duration: videoAsset.duration), of: audio!, at: kCMTimeZero)

                

             catch 
                completion(false,  nil)
            

        

        // * MARK - Composition is ready ----------

        // Create AVMutableVideoCompositionInstruction
        let compositionInstructions = AVMutableVideoCompositionInstruction()
        compositionInstructions.timeRange = CMTimeRange(start: kCMTimeZero, duration: videoAsset.duration)

        // Create an AvmutableVideoCompositionLayerInstruction
        let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction.init(assetTrack: videoTrack!)
        videoLayerInstruction.setTransform(videoAssetTrack.preferredTransform, at: kCMTimeZero)
        compositionInstructions.layerInstructions = [videoLayerInstruction]

        //Add instructions
        let videoComposition = AVMutableVideoComposition()

        let naturalSize : CGSize = videoAssetTrack.naturalSize

        ///Rendering image into video
        let renderWidth = naturalSize.width
        let renderHeight = naturalSize.height

        //Assigning instructions and rendering size
        videoComposition.renderSize = CGSize(width: renderWidth, height: renderHeight)
        videoComposition.instructions = [compositionInstructions]
        videoComposition.frameDuration = CMTime(value: 1, timescale: Int32((videoTrack?.nominalFrameRate)!))

        //Applying image to instruction
        self.applyVideoImage(to: videoComposition, withSize: naturalSize, image: image)

        // Getting the output path
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
        let outputPath = documentsURL?.appendingPathComponent("lastEditedVideo.mp4")
        if FileManager.default.fileExists(atPath: (outputPath?.path)!) 
            do 
                try FileManager.default.removeItem(atPath: (outputPath?.path)!)
            
            catch 
                completion(false, nil)
            
        



        // Create exporter
        let exporter = NextLevelSessionExporter(withAsset: mainMutableComposition)
        exporter.outputURL = outputPath
        exporter.outputFileType = AVFileType.mp4
        exporter.videoComposition = videoComposition

        let compressionDict: [String: Any] = [
            AVVideoAverageBitRateKey: NSNumber(integerLiteral: 2300000),
            AVVideoProfileLevelKey: AVVideoProfileLevelH264BaselineAutoLevel as String
            ]

        exporter.videoOutputConfiguration = [
            AVVideoCodecKey: AVVideoCodecType.h264,
            AVVideoWidthKey: NSNumber(integerLiteral: Int(naturalSize.width)),
            AVVideoHeightKey: NSNumber(integerLiteral: Int(naturalSize.height)),
            AVVideoCompressionPropertiesKey: compressionDict
        ]

        exporter.audioOutputConfiguration = [
            AVFormatIDKey: kAudioFormatMPEG4AAC,
            AVEncoderBitRateKey: NSNumber(integerLiteral: 128000),
            AVNumberOfChannelsKey: NSNumber(integerLiteral: 2),
            AVSampleRateKey: NSNumber(value: Float(44100))
        ]

        completion(true, exporter)
    

我正在使用 NextLevelSessionExporter 导出视频。不管我是否使用默认导出器，大小调整问题仍然存在。

【问题讨论】：

你知道视频是否也被旋转了吗？

你好，不是的。

【参考方案1】：

有一个活跃的错误会阻止您正确导出镜像视频。您需要一些解决方法：

关闭电影输出文件的镜像

需要时手动水平翻转视频：

if needsMirroring == true 

    var transform:CGAffineTransform = CGAffineTransform(scaleX: -1.0, y: 1.0)
    transform = transform.translatedBy(x: -naturalSize.width, y: 0.0)
    transform = transform.rotated(by: CGFloat(Double.pi/2))
    transform = transform.translatedBy(x: 0.0, y: -naturalSize.width)
    videoTransform = transform

我花了好几天才弄明白，希望对你有所帮助。