设置 AVAudioFormat 连接功能崩溃

Question

我一直在尝试使用 AVAudioEngine 播放 16 位流数据。

但是传递给 AVAudioFormat 连接函数总是会导致崩溃。

代码如下：

let AUDIO_OUTPUT_SAMPLE_RATE    = 44100
let AUDIO_OUTPUT_CHANNELS       = 2
let AUDIO_OUTPUT_BITS           = 16
var audioEngine: AVAudioEngine?
var audioPlayer: AVAudioPlayerNode?

...

    audioEngine = AVAudioEngine()
    audioPlayer = AVAudioPlayerNode()

    audioEngine?.attach(audioPlayer!)

    let mixer = audioEngine?.mainMixerNode
    mixer!.outputVolume = 1.0
    let stereoFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: Double(AUDIO_OUTPUT_SAMPLE_RATE), channels: 2, interleaved: false)
    audioEngine!.connect(audioPlayer!, to: mixer!, format: stereoFormat)

...

audioEngine!.connect(...) 崩溃线

我正在使用 Xcode 8 beta 6，OS X El Capitan，而且，这种情况是由模拟器和设备引起的。

这是崩溃消息的一部分：

ERROR:    >avae> AVAudioNode.mm:751: AUSetFormat: error -10868
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'error -10868'

...
3   AVFAudio  0x000000011e0a5630 _Z19AVAE_RaiseExceptionP8NSStringz + 176
4   AVFAudio  0x000000011e0f270d _ZN19AVAudioNodeImplBase11AUSetFormatEP28OpaqueAudioComponentInstancejjP13AVAudioFormat + 213
5   AVFAudio  0x000000011e0f2630 _ZN19AVAudioNodeImplBase15SetOutputFormatEmP13AVAudioFormat + 46
6   AVFAudio  0x000000011e0f9663 _ZN21AVAudioPlayerNodeImpl15SetOutputFormatEmP13AVAudioFormat + 25
7   AVFAudio  0x000000011e099cfd _ZN18AVAudioEngineGraph8_ConnectEP19AVAudioNodeImplBaseS1_jjP13AVAudioFormat + 2377
8   AVFAudio  0x000000011e09d15f _ZN18AVAudioEngineGraph7ConnectEP11AVAudioNodeS1_mmP13AVAudioFormat + 355
9   AVFAudio  0x000000011e0fc80e _ZN17AVAudioEngineImpl7ConnectEP11AVAudioNodeS1_mmP13AVAudioFormat + 348

使用音频文件的缓冲区和格式播放没有问题。

我犯了什么错误？

谢谢。

Answer 1

-10868，a.k.a。 kAudioUnitErr_FormatNotSupported，看来您的 PCMFormatInt16 没有受到重视。将其更改为 .PCMFormatFloat32 确实有效。

Answer 2

来自 Apple，AVAudioPlayerNode

When playing buffers, there's an implicit assumption that the buffers are at the same sample rate as the node’s output format.

然后打印AVAudioPlayerNode的输出格式，即engine.mainMixerNode.inputFormat

    open func connectNodes() {
        print(engine.mainMixerNode.inputFormat(forBus: 0))
        engine.connect(playerNode, to: engine.mainMixerNode, format: readFormat)
    }

结果是

<AVAudioFormat 0x6000024c18b0: 2 ch, 44100 Hz, Float32, non-inter>

所以选择.pcmFormatFloat32，而不是.pcmFormatInt16

OSStatus master website

Answer 3

您不需要自己创建音频格式，

从实际音频数据（pcm缓冲区或音频文件）获取音频格式

the audio format thing from WWDC 2016 , Delivering an Exceptional Audio Experience

The actual audio format theory from WWDC 2015, What's New in Core Audio

输出的实际音频格式

输入的实际音频格式

做音频通道映射，音频位深保持不变

Answer 4

可以使用singed 16位音频格式，但需要先进行转换

// Setup your own format
let inputFormat = AVAudioFormat(
    commonFormat: .pcmFormatInt16,
    sampleRate: 44100,
    channels: AVAudioChannelCount(2),
    interleaved: true
)!

let engine = AVAudioEngine()
// Use system format as output format
let outputFormat = engine.mainMixerNode.outputFormat(forBus: 0)
self.converter = AVAudioConverter(from: inputFormat, to: outputFormat)!

self.playerNode = AVAudioPlayerNode()
engine.attach(playerNode)
engine.connect(playerNode, to: engine.mainMixerNode, format: nil)

...

// Prepare input and output buffer
let inputBuffer = AVAudioPCMBuffer(pcmFormat: inputFormat, frameCapacity: maxSamplesPerBuffer)!
let outputBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat, frameCapacity: maxSamplesPerBuffer)!

// When you fill your Int16 buffer with data, send it to converter
self.converter.convert(to: outputBuffer, error: nil) { inNumPackets, outStatus in
    outStatus.pointee = .haveData
    return inputBuffer
}

// Now in outputBuffer sound in system format and we can play it
self.playerNode.scheduleBuffer(outputBuffer)

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