使用AVAudioEngine离线渲染音频文件

问题描述 投票:1回答:1

我想录制音频文件并通过应用一些效果来保存它。录音还可以,播放此音频效果也不错。问题是,当我尝试将此类音频保存为脱机时,它会生成空音频文件。这是我的代码:

let effect = AVAudioUnitTimePitch()
effect.pitch = -300
self.addSomeEffect(effect)

func addSomeEffect(_ effect: AVAudioUnit) {
    try? AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayAndRecord, with: .defaultToSpeaker)

    let format = self.audioFile.processingFormat
    self.audioEngine.stop()
    self.audioEngine.reset()

    self.audioEngine = AVAudioEngine()
    let audioPlayerNode = AVAudioPlayerNode()


    self.audioEngine.attach(audioPlayerNode)
    self.audioEngine.attach(effect)

    self.audioEngine.connect(audioPlayerNode, to: self.audioEngine.mainMixerNode, format: format)
    self.audioEngine.connect(effect, to: self.audioEngine.mainMixerNode, format: format)

    audioPlayerNode.scheduleFile(self.audioFile, at: nil)
    do {
        let maxNumberOfFrames: AVAudioFrameCount = 8096
        try self.audioEngine.enableManualRenderingMode(.offline,
                                                       format: format,
                                                       maximumFrameCount: maxNumberOfFrames)
    } catch {
        fatalError()
    }


    do {
        try audioEngine.start()
        audioPlayerNode.play()
    } catch {

    }

    let outputFile: AVAudioFile
    do {
        let url = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!.appendingPathComponent("temp.m4a")
        if FileManager.default.fileExists(atPath: url.path) {
            try? FileManager.default.removeItem(at: url)
        }

        let recordSettings = self.audioFile.fileFormat.settings

        outputFile = try AVAudioFile(forWriting: url, settings: recordSettings)
    } catch {
        fatalError()
    }

    let buffer = AVAudioPCMBuffer(pcmFormat: self.audioEngine.manualRenderingFormat,
                                  frameCapacity: self.audioEngine.manualRenderingMaximumFrameCount)!

    while self.audioEngine.manualRenderingSampleTime < self.audioFile.length {
        do {
            let framesToRender = min(buffer.frameCapacity,
                                     AVAudioFrameCount(self.audioFile.length - self.audioEngine.manualRenderingSampleTime))
            let status = try self.audioEngine.renderOffline(framesToRender, to: buffer)
            switch status {
            case .success:
                print("Write to file")
                try outputFile.write(from: buffer)
            case .error:
                fatalError()
            default:
                break
            }
        } catch {
            fatalError()
        }
    }
    print("Finish write")


    audioPlayerNode.stop()
    audioEngine.stop()


    self.outputFile = outputFile
    self.audioPlayer = try? AVAudioPlayer(contentsOf: outputFile.url)

}

AVAudioPlayer无法使用输出URL打开文件。我通过文件系统查看了该文件,它是空的,无法播放。

为AVAudioSession选择不同的类别也不起作用。

感谢帮助!

UPDATE

我切换到输出文件中的记录中使用.caf文件扩展名,它工作正常。知道为什么.m4a不起作用吗?

ios swift avfoundation avaudioplayer avaudioengine
1个回答
2
投票

你需要nil outputFile来刷新标题并关闭m4a文件。

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