Question

我尝试使用Core Audio AudioQueue（Swift 3）播放纯正弦波音。

播放效果很好，但每次调用AudioQueueOutputCallback来填充带有音频数据的新缓冲区时，我都会发出砰砰声。

我的AudioStreamer类看起来像：

let kNumberBuffers = 3

protocol AudioStreamerDelegate {
    func requestAudioData() -> [Float]
}

let sampleRate = 48000.0
let bufferSize = Int(sampleRate) / 50
let bufferByteSize = UInt32(bufferSize * sizeof(Float)) // 20 mili sec of audio

class AudioStreamer {
    var delegate: AudioStreamerDelegate

    var outputQueue: AudioQueueRef?

    var buffers = [AudioQueueBufferRef?](repeatElement(nil, count: kNumberBuffers))

    var streamBasicDescription = AudioStreamBasicDescription(
        mSampleRate: sampleRate,
        mFormatID: kAudioFormatLinearPCM,
        mFormatFlags: kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved,
        mBytesPerPacket: UInt32(sizeof(Float)),
        mFramesPerPacket: 1,
        mBytesPerFrame: UInt32(sizeof(Float)),
        mChannelsPerFrame: 1,
        mBitsPerChannel: UInt32(8 * sizeof(Float)),
        mReserved: 0
    )

    init(delegate: AudioStreamerDelegate) {
        // create new output audio queue
        self.delegate = delegate
    }

    func play() {
        let queue = DispatchQueue.main

        queue.async(execute: {
            let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
            AudioQueueNewOutput(
                &self.streamBasicDescription,
                AudioStreamerOuputCallback,
                selfPointer,
                nil,
                nil,
                0,
                &self.outputQueue
            )

            // allocate buffers
            for i in 0 ..< kNumberBuffers {
                AudioQueueAllocateBuffer(
                    self.outputQueue!,
                    bufferByteSize,
                    &self.buffers[i]
                )

                if let bufferRef = self.buffers[i] {
                    // configure audio buffer
                    let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
                    bufferRef.pointee.mUserData = selfPointer
                    bufferRef.pointee.mAudioDataByteSize = bufferByteSize
                }
            }

            AudioQueuePrime(self.outputQueue!, 0, nil)
            for bufferRef in self.buffers {
                AudioStreamerOuputCallback(userData: unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self), queueRef: self.outputQueue!, buffer: bufferRef!)
            }
            AudioQueueStart(self.outputQueue!, nil)
        })
    }
}

func AudioStreamerOuputCallback(userData: Optional<UnsafeMutablePointer<Void>>, queueRef: AudioQueueRef, buffer: AudioQueueBufferRef) {
    let this = Unmanaged<AudioStreamer>.fromOpaque(OpaquePointer(userData!)).takeUnretainedValue()
    let audioData = this.delegate.requestAudioData()

    memcpy(buffer.pointee.mAudioData, unsafeBitCast(audioData, to: UnsafeMutablePointer<Void>.self), Int(bufferByteSize))
    AudioQueueEnqueueBuffer(queueRef, buffer, 0, nil)
}

ViewController类的音频数据生成器方法，只有＆＃34; play＆＃34;按钮（theta是该ViewController上的存储属性）：

func generateAudioData(frequency: Double) {
    semaphore.wait()

    let amplitude: Double = 0.25

    let theta_increment: Double = 2.0 * M_PI * frequency / sampleRate

    for j in 0 ..< Int(bufferSize) {
        audioData[j] = Float(sin(theta) * amplitude)
        theta += theta_increment

        if theta > 2.0 * M_PI {
            theta -= 2.0 * M_PI
        }
    }
}

问题看起来与this question上的问题类似，但没有人回答。

非常感谢任何帮助。

Answer 1

在输出回调中，您没有生成一组新的音频数据，其中新缓冲区的第一个样本的相位是前一个缓冲区的最后一个样本的增量。

在AudioQueueBuffers之间弹出噪音

1 个答案: