我正在尝试将具有44100采样率的AVAudioPCMBuffer转换为具有48000采样率的AVAudioPCMBuffer,但是在转换时我总是会遇到异常(-50错误)。这是代码:
guard let deviceFormat = AVAudioFormat(standardFormatWithSampleRate: 48000.0, channels: 1) else {
preconditionFailure()
}
// This file is saved as mono 44100
guard let lowToneURL = Bundle.main.url(forResource: "Tone220", withExtension: "wav") else {
preconditionFailure()
}
guard let audioFile = try? AVAudioFile(forReading: lowToneURL) else {
preconditionFailure()
}
let tempBuffer = AVAudioPCMBuffer(pcmFormat: audioFile.processingFormat,
frameCapacity: AVAudioFrameCount(audioFile.length))!
tempBuffer.frameLength = tempBuffer.frameCapacity
do { try audioFile.read(into: tempBuffer) } catch {
assertionFailure("*** Caught: \(error)")
}
guard let converter = AVAudioConverter(from: audioFile.processingFormat, to: deviceFormat) else {
preconditionFailure()
}
guard let convertedBuffer = AVAudioPCMBuffer(pcmFormat: deviceFormat,
frameCapacity: AVAudioFrameCount(audioFile.length)) else {
preconditionFailure()
}
convertedBuffer.frameLength = tempBuffer.frameCapacity
do { try converter.convert(to: convertedBuffer, from: tempBuffer) } catch {
assertionFailure("*** Caught: \(error)")
}
有什么想法吗?
Apple工程师在他们的开发论坛上回答了这个问题。我错过了convert(to:from:)
的AVAudioConverter
变体无法转换采样率的功能,因此您必须使用withInputFrom
变体。上的文档不太清楚,但是我想出了:
private func pcmBufferForFile(filename: String, sampleRate: Float) -> AVAudioPCMBuffer {
guard let newFormat = AVAudioFormat(standardFormatWithSampleRate: Double(sampleRate), channels: 1) else {
preconditionFailure()
}
guard let url = Bundle.main.url(forResource: filename, withExtension: "wav") else {
preconditionFailure()
}
guard let audioFile = try? AVAudioFile(forReading: url) else {
preconditionFailure()
}
guard let tempBuffer = AVAudioPCMBuffer(pcmFormat: audioFile.processingFormat,
frameCapacity: AVAudioFrameCount(audioFile.length)) else {
preconditionFailure()
}
guard let newBuffer = AVAudioPCMBuffer(pcmFormat: newFormat,
frameCapacity: AVAudioFrameCount(audioFile.length)) else {
preconditionFailure()
}
do { try audioFile.read(into: tempBuffer) } catch {
preconditionFailure()
}
guard let converter = AVAudioConverter(from: audioFile.processingFormat, to: newFormat) else {
preconditionFailure()
}
var error: NSError?
converter.convert(to: newBuffer, error: &error, withInputFrom: { (packetCount, statusPtr) -> AVAudioBuffer? in
statusPtr.pointee = .haveData
return tempBuffer
})
if error != nil {
print("*** Conversion error: \(error!)")
}
return newBuffer
}