Question

我的应用需要生成一个音频文件，并且我在上一个Android版本之后编写了文件生成器。在Android上，它使用OKIO来处理IO和iOS，它使用本机NSData。

每个WAV文件都需要一个标题来通知数据阅读器（媒体播放器）的某些参数。

它使用此文件生成器，按照互联网上提供的某些规范写入字节。

//Audio file content, this variable will be used
//to storage the audio data (PCM).
var content = [UInt8]() //This is not empty.
var fileSize: Int = 0 //this is not zero.

//Total size of the file, with the header.
let totalFileSize = fileSize + HEADER_SIZE

//Header data
let header = NSMutableData()

//RIFF
header.append([UInt8]("RIFF".utf8), length: 4)

//Size of the entity file
header.append(Data(bytes: readInt(Int32(totalFileSize).littleEndian)))

//WAVE
header.append([UInt8]("WAVE".utf8), length: 4)

//FMT
header.append([UInt8]("fmt ".utf8), length: 4)

//BITRATE
header.append(Data(bytes: readInt(BITRATE.littleEndian)))

//Audio format
var audioFormat = AUDIO_FORMAT_PCM.littleEndian
header.append(&audioFormat, length: 2)

//Number of channels
var audioChannels = CHANNELS.littleEndian
header.append(&audioChannels, length: 2)

//Sample rate
var sampleRate = SAMPLE_RATE.littleEndian
header.append(&sampleRate, length: 4)

//Byte rate
var byteRate = ((SAMPLE_RATE*UInt32(CHANNELS)*UInt32(BYTES_PER_SAMPLE))/UInt32(8)).littleEndian
header.append(&byteRate, length: 4)

//Block align
var blockAlign = (UInt16(CHANNELS) * UInt16(BYTES_PER_SAMPLE) / UInt16(8)).littleEndian
header.append(&blockAlign, length: 2)

//Bytes per sample
var bytesPerSample = BYTES_PER_SAMPLE.littleEndian
header.append(&bytesPerSample, length: 2)

//Data
header.append([UInt8]("data".utf8), length: 4)

//Size of the audio data
var sizeLittleEndian = UInt32(fileSize).littleEndian
header.append(&sizeLittleEndian, length: 4)

print(header.length) //44

它使用此方法在缓冲区上写入Int：

func readInt(_ i: Int32) -> [UInt8] {
  return [UInt8(truncatingBitPattern: (i >> 24) & 0xff),
          UInt8(truncatingBitPattern: (i >> 16) & 0xff),
          UInt8(truncatingBitPattern: (i >>  8) & 0xff),
          UInt8(truncatingBitPattern: (i      ) & 0xff)]
}

在Android上，生成的文件没有任何问题。但在iOS上这两个参数是错误的。看（Android代码生成的大多数顶级文件，底部是由iOS代码生成的）：

Swift 3

我真的不知道发生了什么，你能帮助我吗？

Answer 1

其中一个主要问题是readInt函数正在返回big-endian，它需要是little-endian。

无论如何，这对我有用。这是我初始化WAV文件的方式。希望它可以帮到某人。

func createHeader() {

    let sampleRate:Int32 = 44100
    let chunkSize:Int32 = 36
    let subChunkSize:Int32 = 16
    let format:Int16 = 1
    let channels:Int16 = 1
    let bitsPerSample:Int16 = 16
    let byteRate:Int32 = sampleRate * Int32(channels * bitsPerSample / 8)
    let blockAlign: Int16 = channels * 2
    let dataSize:Int32 = 0

    let header = NSMutableData()

    header.append([UInt8]("RIFF".utf8), length: 4)
    header.append(intToByteArray(chunkSize), length: 4)

    //WAVE
    header.append([UInt8]("WAVE".utf8), length: 4)

    //FMT
    header.append([UInt8]("fmt ".utf8), length: 4)

    header.append(intToByteArray(subChunkSize), length: 4)
    header.append(shortToByteArray(format), length: 2)
    header.append(shortToByteArray(channels), length: 2)
    header.append(intToByteArray(sampleRate), length: 4)
    header.append(intToByteArray(byteRate), length: 4)
    header.append(shortToByteArray(blockAlign), length: 2)
    header.append(shortToByteArray(bitsPerSample), length: 2)


    header.append([UInt8]("data".utf8), length: 4)

    header.append(intToByteArray(dataSize), length: 4)

    header.write(to: fileURL!, atomically: true)

}

func intToByteArray(_ i: Int32) -> [UInt8] {
    return [
            //little endian
            UInt8(truncatingBitPattern: (i      ) & 0xff),
            UInt8(truncatingBitPattern: (i >>  8) & 0xff),
            UInt8(truncatingBitPattern: (i >> 16) & 0xff),
            UInt8(truncatingBitPattern: (i >> 24) & 0xff)
    ]
}

func shortToByteArray(_ i: Int16) -> [UInt8] {
    return [
        //little endian
        UInt8(truncatingBitPattern: (i      ) & 0xff),
        UInt8(truncatingBitPattern: (i >>  8) & 0xff)
    ]
}

Answer 2

书面totalFileSize在iOS上看起来很大端，而在Android上看起来很小。也许你会{{}}两次？

iOS .littleEndian块看起来也不正常，在Android上data之后有合理的样本值，但在iOS上看起来你已经采取了一些地址CoreAudio结构（可能是data？AudioUnit？ExtAudioFile？）。

生成错误的字节以创建WAV文件

2 个答案: