objective-c - 使用 AVAudioEngine 播放 WAV 数据

Question

目前，我在音频线程上遇到了一个EXC_BAD_ACCESS 错误，我正在尝试推断出了什么问题。

当将 .wav 文件数据从 Data 转换为 AVAudioPCMBuffer 时，是否需要先剥离 RIFF header ？

import AVFoundation

public class Player : NSObject {
  let engine = AVAudioEngine()

  public override init() {
    super.init()
    do {
      let _ = engine.mainMixerNode
      try engine.start()
    } catch {
      print("Player error: \(error)")
    }
  }

  @objc public func play(_ data: Data) {
    let format = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 48000, channels: 2, interleaved: true)!
    let buffer = data.toPCMBuffer(format: format)!

    let player = AVAudioPlayerNode()
    engine.attach(player)
    engine.connect(player, to: engine.mainMixerNode, format: nil)

    player.scheduleBuffer(buffer, at: nil, completionCallbackType: .dataPlayedBack) {
      callbackType in
      // Nothing in here.
    }
    player.play()
  }
}

这是 toPCMBuffer 扩展:

// Taken from: https://stackoverflow.com/a/52731480/2228559
extension Data {
  func toPCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
    let streamDesc = format.streamDescription.pointee
    let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
    guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }

    buffer.frameLength = buffer.frameCapacity
    let audioBuffer = buffer.audioBufferList.pointee.mBuffers

    withUnsafeBytes { addr in
      audioBuffer.mData?.copyMemory(from: addr, byteCount: Int(audioBuffer.mDataByteSize))
    }

    return buffer
  }
}

注意:我不能使用 AVAudioFile，因为 .wav 文件数据是通过网络加载的。

Answer 1

IDK，但如果我播放交错的 AVAudioPCMBuffer，我的 mac 会崩溃，如果音频不是 float 据，则会出现乱码，因此您可以转换为非交错的 float 据:

@objc public func play(_ data: Data) {
    let sampleRate: Double = 48000

    let interleavedFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: sampleRate, channels: 2, interleaved: true)!
    let interleavedBuffer = data.toPCMBuffer(format: interleavedFormat)!

    let nonInterleavedFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: sampleRate, channels: 2, interleaved: false)!
    let nonInterleavedBuffer = AVAudioPCMBuffer(pcmFormat: nonInterleavedFormat, frameCapacity: interleavedBuffer.frameCapacity)!
    nonInterleavedBuffer.frameLength = interleavedBuffer.frameLength

    let converter = AVAudioConverter(from: interleavedFormat, to: nonInterleavedFormat)!
    try! converter.convert(to: nonInterleavedBuffer, from: interleavedBuffer)

    let player = AVAudioPlayerNode()

    engine.attach(player)
    engine.connect(player, to: engine.mainMixerNode, format: nil)

    player.scheduleBuffer(nonInterleavedBuffer, at: nil, completionCallbackType: .dataPlayedBack) {
        callbackType in
        // Nothing in here.
    }

    player.play()
}

extension Data {
    func toPCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
        assert(format.isInterleaved)

        let streamDesc = format.streamDescription.pointee
        let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
        guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }

        buffer.frameLength = buffer.frameCapacity

        let b = UnsafeMutableBufferPointer(start: buffer.int16ChannelData![0], count: buffer.stride * Int(frameCapacity))
        let bytesCopied = self.copyBytes(to: b)
        assert(bytesCopied == count)

        return buffer
    }
}