iOS-PCM文件转WAV文件

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PCM音频文件转WAV音频文件，在PCM数据的文件头加入一个44字节的字段。

WAV的格式为：

iOS-PCM-WAV

里面注意设置参数:

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typedef struct
{
    char chChunkID[4];
    int nChunkSize;
}XCHUNKHEADER; //8

typedef struct
{
    short nFormatTag;
    short nChannels;
    int nSamplesPerSec;
    int nAvgBytesPerSec;
    short nBlockAlign;
    short nBitsPerSample;
}WAVEFORMATX; //16

typedef struct
{
    char chRiffID[4];
    int nRiffSize;
    char chRiffFormat[4];
}RIFFHEADER; //12

void WriteWAVEHeader(NSMutableData* fpwave, int pcmLength)
{
    char tag[10] = "";
    
    // 1. 写RIFF头
    RIFFHEADER riff;
    strcpy(tag, "RIFF");
    memcpy(riff.chRiffID, tag, 4);
    riff.nRiffSize = pcmLength + 44 - 8; //减去RIFF和nRiffSize
    strcpy(tag, "WAVE");
    memcpy(riff.chRiffFormat, tag, 4);
    [fpwave appendBytes:&riff length:sizeof(RIFFHEADER)];
    
    // 2. 写FMT块
    XCHUNKHEADER chunk;
    WAVEFORMATX wfx;
    strcpy(tag, "fmt ");
    memcpy(chunk.chChunkID, tag, 4);
    chunk.nChunkSize = sizeof(WAVEFORMATX);
    [fpwave appendBytes:&chunk length:sizeof(XCHUNKHEADER)];
    memset(&wfx, 0, sizeof(WAVEFORMATX));
    wfx.nFormatTag = 1;
    wfx.nChannels = 2;
    wfx.nSamplesPerSec = 44100;
    wfx.nBitsPerSample = 16; // 16位
    wfx.nBlockAlign = wfx.nChannels * wfx.nBitsPerSample / 8;
    wfx.nAvgBytesPerSec = wfx.nBlockAlign * wfx.nSamplesPerSec;
    [fpwave appendBytes:&wfx length:sizeof(WAVEFORMATX)];
    
    // 3. 写data块头
    strcpy(tag, "data");
    memcpy(chunk.chChunkID, tag, 4);
    chunk.nChunkSize = pcmLength;
    [fpwave appendBytes:&chunk length:sizeof(XCHUNKHEADER)];
}

+ (NSData*)pcmToWav:(NSData*)pcmData totalLength:(int)totalLength
{
    NSMutableData *wavData = [NSMutableData new];
    WriteWAVEHeader(wavData, (int)totalLength);
    NSLog(@"%d", (int)wavData.length);
    [wavData appendData:pcmData];
    return wavData;
}