从 AudioQueueBufferRef 输出队列回调获取音频浮点数

Question

我被困了好几天，试图从一个简单的 mp3 音频队列输出中获取正确的音频浮动 AudioQueueBufferRef 使用 .mAudioData

let callback : @convention(c) (_ userData : UnsafeMutableRawPointer?,
    _ queue : AudioQueueRef,
    _ bufferToFill : AudioQueueBufferRef) -> Void =
    { (userData, queue, bufferToFill) in
        guard let myInfo = userData?.assumingMemoryBound(to: myInfo.self) else {return}
        Utility.check(AudioFileReadPacketData(myInfo.pointee.playbackFile! ,              // AudioFileID
            false,                                     // use cache?
            &numBytes,                                 // initially - buffer capacity, after - bytes actually read
            myInfo.pointee.packetDescs,                // pointer to an array of PacketDescriptors
            myInfo.pointee.packetPosition,             // index of first packet to be read
            &nPackets,                                 // number of packets
            bufferToFill.pointee.mAudioData),          // output buffer
            operation: "AudioFileReadPacketData failed")
      let size = Int((bufferToFill.pointee.mAudioDataBytesCapacity) / 2 )
      let array = Array(UnsafeMutableBufferPointer(start: bufferToFill.pointee.mAudioData.assumingMemoryBound(to: Int16.self), count: size))
      print(array[0...5],"int16")
      //to floats
      let numSamples = array.count / MemoryLayout<Int16>.size //2
      var factor = Float(Int16.max)
      var floatsArr: [Float] = Array(repeating: 0.0, count: numSamples)
      var scaledFloats: [Float] = Array(repeating: 0.0, count: numSamples)
      print(array[0...20],scaledFloats.count,"int16")
      vDSP_vflt16(array, 1, &floatsArr, 1, vDSP_Length(numSamples))
      print(array[0...20],scaledFloats.count,"floats")
      vDSP_vsdiv(&floatsArr, 1, &factor, &scaledFloats, 1, vDSP_Length(numSamples))//scaling
      print(scaledFloats[0...20],scaledFloats.count, "scaledfloats n")

}

我得到了错误的浮动，但我能够成功播放。我想从 AudioQueueBufferRef 绘制波形

谢谢！如果你想尝试一下https://github.com/masaldana2/getmAudioData

Answer 1

尝试替换：

let numSamples = array.count / MemoryLayout<Int16>.size //2

由：

let numSamples = array.count

我相信您的浮点缓冲器是预期大小的一半，否则。

这是我用于测试的代码子集的修改后的独立版本：

import Foundation
import Accelerate
let size = 7
var data : [Int16] = [ 0, 1, 2, 3, 4, -Int16.max, Int16.max ]
let array = Array(UnsafeMutableBufferPointer(start: &data, count: size))
var floatsArr:    [Float] = Array(repeating: 0.0, count: array.count)
var scaledFloats: [Float] = Array(repeating: 0.0, count: array.count)
vDSP_vflt16(array, 1, &floatsArr, 1, vDSP_Length(array.count))
var factor = Float(Int16.max)
vDSP_vsdiv(floatsArr, 1, &factor, &scaledFloats, 1, vDSP_Length(array.count))
print(       array[0 ...        array.count - 1],        array.count, "int16")
print(   floatsArr[0 ...    floatsArr.count - 1],    floatsArr.count, "float")
print(scaledFloats[0 ... scaledFloats.count - 1], scaledFloats.count, "scaled")

及其输出：

[0, 1, 2, 3, 4, -32767, 32767] 7 int16
[0.0, 1.0, 2.0, 3.0, 4.0, -32767.0, 32767.0] 7 float
[0.0, 3.05185094e-05, 6.10370189e-05, 9.15555283e-05, 0.000122074038, -1.0, 1.0] 7 scaled