Question

我有一个使用AVAudioSession来录制音频并对其进行分析以确定频率以进行调谐的应用。问题是AVAudioSession.sharedInstance().sampleRate报告的采样率与实际记录率不符。

在某些设备（iPhone SE和iPad Mini 2）上，报告的采样率为44,100，与实际数据匹配。但是在某些其他设备（iPhone 6S，iPhone 8）上，系统报告的采样率为48,000，但只有将采样解释为好像每秒记录44,100个采样时，返回的采样才有意义。

我尝试用AVAudioSession.sharedInstance().setPreferredSampleRate()控制采样率，但这似乎完全没有效果。

为什么报告的汇率与实际数据不符？

以下是一些代码：

class Myrecorder: NSObject, AVCaptureAudioDataOutputSampleBufferDelegate  {

    let session : AVCaptureSession!

    override init() {
        session = AVCaptureSession()
        super.init()
    }

    enum SetupResult {
        case OK, noInput, noPermission, internalError, waiting
    }

    var isSetup:Bool = false

    func setup( callback:@escaping (()->Bool)) -> SetupResult {
        do {
            let sharedInstance = AVAudioSession.sharedInstance()
            try sharedInstance.setCategory( AVAudioSessionCategoryPlayAndRecord )
        } catch {
            return SetupResult.internalError
        }
        let device = AVCaptureDevice.default( for: AVMediaType.audio )
        guard (device != nil) else {
            return SetupResult.noInput
        }
        let status = AVCaptureDevice.authorizationStatus(  for:AVMediaType.audio )
        guard status != .denied else {
            return SetupResult.noPermission
        }
        guard status != .notDetermined else {
            AVCaptureDevice.requestAccess(for: AVMediaType.audio ){ granted in
                _ = callback()
            }
            return SetupResult.waiting
        }
        var input : AVCaptureDeviceInput
        do {
            try device!.lockForConfiguration()
            try input = AVCaptureDeviceInput( device: device! )
            device!.unlockForConfiguration()
        } catch {
            device!.unlockForConfiguration()
            return SetupResult.internalError
        }
        let output = AVCaptureAudioDataOutput()
        output.setSampleBufferDelegate(self, queue: Intonia.realTimeQueue)
        session.beginConfiguration()
        guard session.canAddInput( input ) else {
            return SetupResult.internalError
        }
        session.addInput( input )
        guard session.canAddOutput( output ) else {
            return SetupResult.internalError
        }
        session.addOutput( output )
        session.commitConfiguration()
        isSetup = true;
        return SetupResult.OK
    }

    static func getSampleRate() -> Double {
        return AVAudioSession.sharedInstance().sampleRate
    }

    func captureOutput(_ captureOutput: AVCaptureOutput,
                       didOutput sampleBuffer: CMSampleBuffer,
                       from connection: AVCaptureConnection){
        var buffer: CMBlockBuffer? = nil
        var audioBufferList = AudioBufferList(
            mNumberBuffers: 1,
            mBuffers: AudioBuffer(mNumberChannels: 1, mDataByteSize: 0, mData: nil)
        )
        CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
            sampleBuffer,
            nil,
            &audioBufferList,
            MemoryLayout<AudioBufferList>.size,
            nil,
            nil,
            UInt32(kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment),
            &buffer
        )
        let abl = UnsafeMutableAudioBufferListPointer(&audioBufferList)
        for buff in abl {
            let samples = UnsafeBufferPointer<Int16>(
                start: UnsafePointer(OpaquePointer(buff.mData)),
                count: Int(buff.mDataByteSize)/MemoryLayout<Int16>.size)
            let newSamples = [Int16](samples)
            MyApp.putSamples_A(samples: newSamples )
        }
    }

    func record() {
        MyApp.realTimeQueue.async {
            self.session.startRunning()
        }
    }

    func pause() {
        session.stopRunning()
    }    
}

在iPhone上获取采样率

0 个答案: