AudioFileReadPacketData returns -50 when passed valid file

问题

I've spent some time attempting to debug this on my own but I can't seem to get the AudioFileReadPacketData to correctly read the passed in data. This is based almost directly off of the Apple AudioQueueServices Guide.

class SVNPlayer: SVNPlayback {
  var queue: AudioQueueRef?
  var audioFormat: AudioStreamBasicDescription!
  var playbackFile: AudioFileID?
  var packetDesc: AudioStreamPacketDescription!
  var isDone = false
  var packetPosition: Int64 = 0
  var numPacketsToRead = UInt32()

  private let callback: AudioQueueOutputCallback = { aqData, inAQ, inBuffer in

    guard let userData = aqData else { return }
    let audioPlayer = Unmanaged<SVNPlayer>.fromOpaque(userData).takeUnretainedValue()
    var buffer = inBuffer.pointee
    if audioPlayer.isDone { return }
    var numBytes: UInt32 = 0
    var nPackets = audioPlayer.numPacketsToRead

this is the line that is throwing -50

    var code = AudioFileReadPacketData(audioPlayer.playbackFile!, false, &numBytes, &audioPlayer.packetDesc!, audioPlayer.packetPosition, &nPackets, buffer.mAudioData)

which is in turn crashing on AudioQueueEnqueueBuffer

    if nPackets > 0 {
      buffer.mAudioDataByteSize = numBytes
      AudioQueueEnqueueBuffer(inAQ, &buffer, nPackets, &audioPlayer.packetDesc!)
      audioPlayer.packetPosition += Int64(nPackets)
    } else {
      AudioQueueStop(inAQ, false)
      audioPlayer.isDone = true
    }
  }

  func prepareToPlayback(with fileURL: URL) throws {

    let pointer = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque()) // get an unmananged reference to self

    var format = AudioStreamBasicDescription()

    var formatSize = UInt32(MemoryLayout<AudioStreamBasicDescription>.stride)

    var audioFileID: AudioFileID? // open the recorded file

    try osStatus { AudioFileOpenURL(fileURL as CFURL, AudioFilePermissions.readPermission, 0, &audioFileID) }

    playbackFile = audioFileID  // get the full audio data format from the file

    try osStatus { AudioFileGetProperty(playbackFile!, kAudioFilePropertyDataFormat, &formatSize, &format) }

    try osStatus { AudioQueueNewOutput(&format, callback, pointer, nil, nil, 0, &queue) }

    var bufferByteSize = UInt32()
    try deriveBufferByteSize(with: playbackFile!,
                             format: format,
                             duration: 0.5,
                             outBufferByteSize: &bufferByteSize,
                             outNumPackets: &numPacketsToRead)
    let isFormatVBR = format.mBytesPerPacket == 0 || format.mFramesPerPacket == 0
    if isFormatVBR {
      packetDesc = AudioStreamPacketDescription(mStartOffset: 0, mVariableFramesInPacket: numPacketsToRead, mDataByteSize: UInt32(MemoryLayout<AudioStreamPacketDescription>.stride)) // this may fail i dunno
    }  // we don't provide packet descriptions for constant bit rate formats (like linear PCM)
    packetDesc = AudioStreamPacketDescription()

    try copyEncoderCookieToQueue(with: playbackFile!, queue: &queue!)

    var bufferRef: AudioQueueBufferRef?
    isDone = false
    packetPosition = 0
    for _ in 0..<3 {

      try osStatus { AudioQueueAllocateBuffer(queue!, bufferByteSize, &bufferRef) }

      guard let buffer = bufferRef else { print("couldn't get buffer"); return }
      callback(pointer, queue!, buffer)
      if isDone {
        break
      }
    }
  }

  func start() throws {
    try osStatus { AudioQueueStart(queue!, nil) }

    repeat {
      CFRunLoopRunInMode(CFRunLoopMode.defaultMode, 0.25, false)
    } while !isDone

    CFRunLoopRunInMode(CFRunLoopMode.defaultMode, 2, false)
    isDone = true
    AudioQueueStop(queue!, true)
    //clean up
    AudioQueueDispose(queue!, true)
    AudioFileClose(playbackFile!)

  }

  // we only use time here as a guideline
  // we're really trying to get somewhere between 16K and 64K buffers, but not allocate too much if we don't need it
  private func deriveBufferByteSize(with file: AudioFileID, format: AudioStreamBasicDescription, duration: Double, outBufferByteSize: inout UInt32, outNumPackets: inout UInt32) throws {
    // we need to calculate how many packets we read at a time, and how big a buffer we need.
    // we base this on the size of the packets in the file and an approximate duration for each buffer.
    //
    // first check to see what the max size of a packet is, if it is bigger than our default
    // allocation size, that needs to become larger

    var maxPacketSize: UInt32 = 0
    var propertySize = UInt32(MemoryLayout<UInt32>.size(ofValue: maxPacketSize))

    try osStatus { AudioFileGetProperty(file, kAudioFilePropertyPacketSizeUpperBound, &propertySize, &maxPacketSize) }

    let maxBufferSize: Int = 0x10000
    let minBufferSize: Int = 0x4000
    let uMaxBufferSize = UInt32(maxBufferSize)
    let uMinBufferSize = UInt32(minBufferSize)

    if format.mFramesPerPacket == 0 {
      let numPacketesForTime = format.mSampleRate / Double(format.mFramesPerPacket) * duration
      outBufferByteSize = UInt32(numPacketesForTime) * maxPacketSize
    } else {
      // if frames per packet is zero, then the codec has no predictable packet == time
      // so we can't tailor this (we don't know how many Packets represent a time period
      // we'll just return a default buffer size
      outBufferByteSize = uMaxBufferSize > maxPacketSize ? uMaxBufferSize : maxPacketSize
    }

    // limit the size to our default
    if outBufferByteSize > uMaxBufferSize && outBufferByteSize > maxPacketSize {
      outBufferByteSize = uMaxBufferSize
    }
      // make sure it doesnt get too small - we dont want to save small chunks to disk
    else if outBufferByteSize < uMinBufferSize {
      outBufferByteSize = uMinBufferSize
    }
    outNumPackets = outBufferByteSize / maxPacketSize
  }

  private func copyEncoderCookieToQueue(with file: AudioFileID, queue: inout AudioQueueRef) throws {
    var propertySize = UInt32()

    try osStatus { AudioFileGetPropertyInfo(file, kAudioFilePropertyMagicCookieData, &propertySize, nil) }

    if propertySize > 0 {
      var magicCookie = UInt8(MemoryLayout<UInt8>.size(ofValue: UInt8(propertySize)))
      try osStatus { AudioFileGetProperty(file, kAudioFilePropertyMagicCookieData, &propertySize, &magicCookie) }
      try osStatus { AudioQueueSetProperty(queue, kAudioQueueProperty_MagicCookie, &magicCookie, propertySize) }
    }
  }
}

回答1:

I think the problem is that you're trying to read 0 bytes of packet data - numBytes is actually for both input and output.

Try setting it to this

var numBytes = buffer.mAudioDataBytesCapacity

来源：https://stackoverflow.com/questions/44316380/audiofilereadpacketdata-returns-50-when-passed-valid-file