WAV文件格式

(🗒️)

WAV是一种常用的音频文件格式, 主要有信息头+数据构成, 数据一般是PCM(脉冲编码调制), 这个信息头就是对PCM数据的描述, 包括采样率、数据长度、通道数、每个通道的字节数等等信息, 播放器依靠这些信息才能正确播放PCM内容.

PCM数据采集

一般的输入设备, 如麦克风提供PCM格式的数据输出，PCM格式的数据是无损的, 基本上所有的播放设备都支持播放, 因为是原始的声音信息, 由模拟信号转换而来，数据中存在大量时间冗余和空间冗余。数据量比较大。

PCM生成WAV

WAV 格式

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#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <sys/stat.h>
#include <ctype.h>

#pragma pack(1)
typedef unsigned char byte;
typedef struct WAVHeader {
    // big endian
    char no[4];
    // little endian
    uint32_t size;
    // big endian
    char format[4];
    char formatTag[4];
    // little endian
    uint32_t formatTagSize;
    // little endian
    uint16_t audioFormat;
    uint16_t audioChannel;
    uint32_t audioSampleRate;
    uint32_t audioByteRate;
    uint16_t audioBlockAlign;
    uint16_t audioBitsPerSample;

    // big endian
    char dataTag[4];
    uint32_t dataTagSize;
} WAVHeader;
#pragma pack()

// #define s2l(s) (s << 8 & 0xFF00) | (s >> 8 & 0xFF)
// #define i2l(i) \
//     (i >> 24 & 0xFF) | (i >> 8 & 0xFF00) | (i << 8 & 0xFF0000) | \
//         (i << 24 & 0xFF000000)
#define s2l(s) s
#define i2l(i) i

int main(int argc, char ** argv) {
    if (argc != 3) {
        printf("Usage: ./wav <pcm-file-path> <save-wav-file-path>\n");
        return -1;
    }

    const char * wavPath = argv[2];
    FILE * file          = fopen(wavPath, "w+b");
    if (!file) {
        fprintf(stderr, "error occur %s\n", strerror(errno));
        return -1;
    }

    const char * dataPath = argv[1];
    FILE * pcmFile        = fopen(dataPath, "r");
    if (!pcmFile) {
        fprintf(stderr, "error occur %s\n", strerror(errno));
        return -1;
    }

    struct stat pcmFileStat;
    fstat(pcmFile->_file, &pcmFileStat);
    size_t dataSize = pcmFileStat.st_size;
    printf("pcm file size %ld\n", dataSize);

    WAVHeader header = {.no                 = {'R', 'I', 'F', 'F'},
                        .size               = i2l((dataSize + 36)),
                        .format             = {'W', 'A', 'V', 'E'},
                        .formatTag          = {'f', 'm', 't', ' '},
                        .formatTagSize      = i2l(16),
                        .audioFormat        = s2l(1),
                        .audioChannel       = s2l(1),
                        .audioSampleRate    = i2l(44100),
                        .audioByteRate      = i2l(88200),
                        .audioBlockAlign    = s2l(4),
                        .audioBitsPerSample = s2l(16),
                        .dataTag            = {'d', 'a', 't', 'a'},
                        .dataTagSize        = i2l(dataSize)};

    fwrite(&header, sizeof(WAVHeader), 1, file);
    byte * buff  = new byte[128];
    int sizeRead = 0;
    while ((sizeRead = fread(buff, 1, 128, pcmFile)) != 0) {
        fwrite(buff, 1, sizeRead, file);
    }
    delete[] buff;
    fclose(pcmFile);
    fclose(file);
    return 0;
}

参考链接