ios - 处理格式和数据正确的音频文件时出错

Question

我正在尝试将处理音频 url 与视频 url 合并。我已经进行了音频以使用audioEngine.renderOffline方法更改音高值。但输出音频文件返回 nil 值audioAsset.tracks(withMediaType: .audio).first（同时 audioAsset.metadata 为空）。由于 nil 值，我无法合并视频和音频。

注意：我可以共享继续的音频文件，它可以工作，但当我在AVAudioPlayer.

我也尝试使用installTapOnBus方法进行音频，但每次都没有得到正确的输出文件。

请帮我解决上述错误。

代码如下：

func extractAudio(url:URL) {
        // Create a composition
                let composition = AVMutableComposition()
                let asset = AVURLAsset(url: url)
                do {

                    guard let audioAssetTrack = asset.tracks(withMediaType: AVMediaType.audio).first else { return }
                    guard let audioCompositionTrack = composition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: kCMPersistentTrackID_Invalid) else { return }
                    try audioCompositionTrack.insertTimeRange(audioAssetTrack.timeRange, of: audioAssetTrack, at: CMTime.zero)
                } catch {
                    print(error)
                }

                // Get url for output
                let outputUrl = URL(fileURLWithPath: NSTemporaryDirectory() + "out.m4a")
                if FileManager.default.fileExists(atPath: outputUrl.path) {
                    try? FileManager.default.removeItem(atPath: outputUrl.path)
                }

                // Create an export session
                let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)!
                exportSession.outputFileType = AVFileType.m4a
                exportSession.outputURL = URL.init(fileURLWithPath: outputUrl.path)
                exportSession.timeRange = CMTimeRangeMake(start: CMTime.zero, duration: asset.duration)
                // Export file
                exportSession.exportAsynchronously {
                    guard case exportSession.status = AVAssetExportSession.Status.completed else { return }
                    self.sourceFile = try! AVAudioFile(forReading: outputUrl)
                    self.format = self.sourceFile.processingFormat
                    self.playAndRecord(pitch: -500, rate: 1.0, reverb: 10, echo: 1.0)
                }
    }

func playAndRecord(pitch : Float, rate: Float, reverb: Float, echo: Float) {
        let engine = AVAudioEngine()
        let player = AVAudioPlayerNode()
        let reverbEffect = AVAudioUnitReverb()
        let pitchEffect = AVAudioUnitTimePitch()
        let playbackRateEffect = AVAudioUnitVarispeed()

        engine.attach(player)
        engine.attach(reverbEffect)
        engine.attach(pitchEffect)
        engine.attach(playbackRateEffect)

        // Set the desired reverb parameters.
        reverbEffect.loadFactoryPreset(.mediumHall)
        reverbEffect.wetDryMix = reverb
        
        pitchEffect.pitch = pitch
        
        playbackRateEffect.rate = rate
        
        
        // Connect the nodes.
        engine.connect(player, to: reverbEffect, format: format)
        engine.connect(reverbEffect, to: pitchEffect, format: format)
        engine.connect(pitchEffect, to: playbackRateEffect, format: format)
        engine.connect(playbackRateEffect, to: engine.mainMixerNode, format: format)

        // Schedule the source file.
        player.scheduleFile(sourceFile, at: nil)
        
        do {
            // The maximum number of frames the engine renders in any single render call.
            let maxFrames: AVAudioFrameCount = 4096
            try engine.enableManualRenderingMode(.offline, format: format,
                                                 maximumFrameCount: maxFrames)
        } catch {
            fatalError("Enabling manual rendering mode failed: \(error).")
        }
        
        do {
            try engine.start()
            player.play()
        } catch {
            fatalError("Unable to start audio engine: \(error).")
        }
        // The output buffer to which the engine renders the processed data.
        let buffer = AVAudioPCMBuffer(pcmFormat: engine.manualRenderingFormat,
                                      frameCapacity: engine.manualRenderingMaximumFrameCount)!


        var outputFile: AVAudioFile
        do {
            let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
            let outputURL = documentsURL.appendingPathComponent("EDittedFile.m4a")
            
            outputFile = try AVAudioFile(forWriting: outputURL, settings: sourceFile.fileFormat.settings, commonFormat: .pcmFormatInt32,interleaved: true)
        } catch {
            fatalError("Unable to open output audio file: \(error).")
        }
        
        // Process the file
        while engine.manualRenderingSampleTime < sourceFile.length {
            do {
                let frameCount = sourceFile.length - engine.manualRenderingSampleTime
                let framesToRender = min(AVAudioFrameCount(frameCount), buffer.frameCapacity)
                
                let status = try engine.renderOffline(framesToRender, to: buffer)
                switch status {
                case .success:
                    // The data rendered successfully. Write it to the output file.
                    try outputFile.write(from: buffer)
                case .insufficientDataFromInputNode:
                    // Applicable only when using the input node as one of the sources.
                    break
                case .cannotDoInCurrentContext:
                    // The engine couldn't render in the current render call.
                    // Retry in the next iteration.
                    break
                case .error:
                    // An error occurred while rendering the audio.
                    fatalError("The manual rendering failed.")
                }
            } catch {
                fatalError("The manual rendering failed: \(error).")
            }
        }
    
        print("finished")
        let asset = AVURLAsset.init(url: outputFile.url)
        print(asset.tracks(withMediaType: .audio))
        player.stop()
        engine.stop()
   }

提前致谢。

标签： iosswiftaudiovideoavaudioengine