ios - 使用 Swift 流式传输音频
问题描述
我正在开发一个应用程序,它应该记录用户的声音并通过 MQTT 协议将其流式传输到自定义设备。自定义设备的音频规范:little-endian、无符号、16 位 LPCM,采样率为 8khz。每个数据包应为 1000 字节。
我对 AudioEngine 不熟悉,我发现这个代码示例适合我的情况:
func startRecord() {
audioEngine = AVAudioEngine()
let bus = 0
let inputNode = audioEngine.inputNode
let inputFormat = inputNode.outputFormat(forBus: bus)
var streamDescription = AudioStreamBasicDescription()
streamDescription.mFormatID = kAudioFormatLinearPCM.littleEndian
streamDescription.mSampleRate = 8000.0
streamDescription.mChannelsPerFrame = 1
streamDescription.mBitsPerChannel = 16
streamDescription.mBytesPerPacket = 1000
let outputFormat = AVAudioFormat(streamDescription: &streamDescription)!
guard let converter: AVAudioConverter = AVAudioConverter(from: inputFormat, to: outputFormat) else {
print("Can't convert in to this format")
return
}
inputNode.installTap(onBus: 0, bufferSize: 1024, format: inputFormat) { (buffer, time) in
print("Buffer format: \(buffer.format)")
var newBufferAvailable = true
let inputCallback: AVAudioConverterInputBlock = { inNumPackets, outStatus in
if newBufferAvailable {
outStatus.pointee = .haveData
newBufferAvailable = false
return buffer
} else {
outStatus.pointee = .noDataNow
return nil
}
}
let convertedBuffer = AVAudioPCMBuffer(pcmFormat: outputFormat, frameCapacity: AVAudioFrameCount(outputFormat.sampleRate) * buffer.frameLength / AVAudioFrameCount(buffer.format.sampleRate))!
var error: NSError?
let status = converter.convert(to: convertedBuffer, error: &error, withInputFrom: inputCallback)
assert(status != .error)
print("Converted buffer format:", convertedBuffer.format)
}
audioEngine.prepare()
do {
try audioEngine.start()
} catch {
print("Can't start the engine: \(error)")
}
}
但是目前,转换器无法将输入格式转换为我的输出格式,我不明白为什么。如果我将输出格式更改为类似的内容:
let outputFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 8000.0, channels: 1, interleaved: false)!
然后它工作。
解决方案
你streamDescription
错了,你没有填写所有的字段,而且mBytesPerPacket
错了——这不是你的协议要求的那种数据包。对于未压缩的音频(如 LPCM)AudioStreamBasicDescription
,要求此字段为 1。如果您的协议要求样本以 1000 个为一组,那么您将不得不这样做。
尝试这个
var streamDescription = AudioStreamBasicDescription()
streamDescription.mSampleRate = 8000.0
streamDescription.mFormatID = kAudioFormatLinearPCM
streamDescription.mFormatFlags = kAudioFormatFlagIsSignedInteger // no endian flag means little endian
streamDescription.mBytesPerPacket = 2
streamDescription.mFramesPerPacket = 1
streamDescription.mBytesPerFrame = 2
streamDescription.mChannelsPerFrame = 1
streamDescription.mBitsPerChannel = 16
streamDescription.mReserved = 0
推荐阅读
- threadpool - HikariPoolMXBean - getThreadsAwaitingConnection - 线程指的是什么?
- r - 使用“__”时禁止加粗
- json - 如何将 xml 正文转换为 json 以在脚本中介 wso2 中使用 getPayloadJSON()?
- c++ - 如何允许二进制文件与多个共享库版本一起运行
- sql - 如何从不同的表中获取记录并忽略 SQL 中的重复日期?
- javascript - WebSocket 响应函数执行
- python - 如何控制 mpl_toolkits 底图的边距?
- python - 更改整个窗口的鼠标光标形状(应用程序窗口内部和外部)
- java - java.sql.SQLIntegrityConstraintViolationException: ORA-00001
- javascript - Testcafe:多个没有存储事件的 Windows