如何从 Swift 中的音频文件生成浮点数组

Question

我想将 mp3 和 wav 音频文件加载为浮点数或双精度数组，类似于 scipy 中的 io.wavfile.read 函数。我可以通过将音频流写入缓冲区来处理麦克风数据或播放音频。但是，我不确定如何一次加载所有音频文件的数据。

-- 更新

对于将来使用音频信号数据的任何人，这里有一个功能可以解决问题。它基于 Rhythmic Fistman 的回答。

    func loadAudioSignal(audioURL: NSURL) -> (signal: [Float], rate: Double, frameCount: Int) {
        let file = try! AVAudioFile(forReading: audioURL)
        let format = AVAudioFormat(commonFormat: .PCMFormatFloat32, sampleRate: file.fileFormat.sampleRate, channels: file.fileFormat.channelCount, interleaved: false)
        let buf = AVAudioPCMBuffer(PCMFormat: format, frameCapacity: UInt32(file.length))
        try! file.readIntoBuffer(buf) // You probably want better error handling
        let floatArray = Array(UnsafeBufferPointer(start: buf.floatChannelData[0], count:Int(buf.frameLength)))
        return (signal: floatArray, rate: file.fileFormat.sampleRate, frameCount: Int(file.length))
    }

Answer 1

AVAudioFile内置于iOS（和OS X），非常方便，还会为你做格式转换：

import AVFoundation
// ...

let url = NSBundle.mainBundle().URLForResource("your audio file", withExtension: "wav")
let file = try! AVAudioFile(forReading: url!)
let format = AVAudioFormat(commonFormat: .PCMFormatFloat32, sampleRate: file.fileFormat.sampleRate, channels: 1, interleaved: false)

let buf = AVAudioPCMBuffer(PCMFormat: format, frameCapacity: 1024)
try! file.readIntoBuffer(buf)

// this makes a copy, you might not want that
let floatArray = Array(UnsafeBufferPointer(start: buf.floatChannelData[0], count:Int(buf.frameLength)))

print("floatArray \(floatArray)\n")

遗憾的是，对于双打来说，用.PCMFormatFloat64 替换.PCMFormatFloat32 似乎是不够的，因为AVAudioPCMBuffer 没有float64ChannelData 方法。

更新因为我不太了解swift

您可以通过使用UnsafeBufferPointer 来避免复制数组，这是一个非常好的集合类型：

let floatArray = UnsafeBufferPointer(start: buf.floatChannelData[0], count:Int(buf.frameLength))

Answer 2

要找到有关UnsafeBufferPointer 的所有信息真的很棘手

我在这里发布 Swift 5.0 的更新代码

if let url = Bundle.main.url(forResource: "silence", withExtension: "mp3") {
    let file = try! AVAudioFile(forReading: url)
    if let format = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: file.fileFormat.sampleRate, channels: 1, interleaved: false) {
        if let buf = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: 1024) {
            try! file.read(into: buf)

            // this makes a copy, you might not want that
            let floatArray = UnsafeBufferPointer(start: buf.floatChannelData![0], count:Int(buf.frameLength))
            // convert to data
            var data = Data()
            for buf in floatArray {
                data.append(withUnsafeBytes(of: buf) { Data($0) })
            }
            // use the data if required.
        }
    }
}

希望对你有帮助:)

Answer 3

以上答案对我不起作用，我使用的是 Swift5，在这里找到了适合我的扩展：https://gist.github.com/jtodaone/f2fa59c19794811dbe989dff65a772bc

这也是我在 Playground 上使用代码的方式

import UIKit
import AVFoundation

let filePath: String = Bundle.main.path(forResource: "nameOfFile", ofType: "wav")!
print("\(filePath)")
let fileURL: NSURL = NSURL(fileURLWithPath: filePath)
let audioFile = try AVAudioFile(forReading: fileURL as URL)
let audioFormat = audioFile.processingFormat
let audioFrameCount = UInt32(audioFile.length)
let audioFileBuffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: audioFrameCount)

try audioFile.read(into: audioFileBuffer!)

extension AudioBuffer {
    func array() -> [Float] {
        return Array(UnsafeBufferPointer(self))
    }
}

extension AVAudioPCMBuffer {
    func array() -> [Float] {
        return self.audioBufferList.pointee.mBuffers.array()
    }
}

extension Array where Element: FloatingPoint {
    mutating func buffer() -> AudioBuffer {
        return AudioBuffer(mNumberChannels: 1, mDataByteSize: UInt32(self.count * MemoryLayout<Element>.size), mData: &self)
    }
}

let array = audioFileBuffer?.array()
print(array?.count) //Optional(2705408)

Answer 4

我已将代码从@rhythmicfistman 更新为Swift5。大约需要进行十几个更改：显然swift 世界的情况发生了巨大变化。

func readWavIntoFloats(fname: String, ext: String) -> [Float] {

    let url = Bundle.main.url(forResource: fname, withExtension: ext)
    let file = try! AVAudioFile(forReading: url!)
    let format = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: file.fileFormat.sampleRate, channels: 1, interleaved: false) ?? <#default value#>

    let buf = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: 1024)!
    try! file.read(into: buf)

    // this makes a copy, you might not want that
    let floatArray = Array(UnsafeBufferPointer(start: buf.floatChannelData?[0], count:Int(buf.frameLength)))

    return floatArray

}