更改 wav 文件的采样率和比特率而不会遇到打开文件的问题？

Posted 2023-02-25

【中文标题】更改 wav 文件的采样率和比特率而不会遇到打开文件的问题？

【英文标题】：Changing samplerate and byterate of a wav file without encountering problems opening the file?

【发布时间】：2015-07-12 21:34:33

【问题描述】：

我正在尝试将 503,196 字节的 wav 文件的内容写入另一个文件，并将采样率/字节率加倍以使速度加倍。但是，我无法从输入文件中读取数据并将其写入输出文件。这是我的代码：

#include <stdio.h>

int main() 
    struct WAVE 
           char ChunkID[4];
           unsigned int ChunkSize;
           char Format[4];
           char Subchunk1ID[4];
           unsigned int Subchunk1Size;
           unsigned short int AudioFormat;
           unsigned short int NumChannels;
           unsigned int SampleRate;
           unsigned int ByteRate;
           unsigned short int BlockAlign;
           unsigned short int BitsPerSample;
           char Subchunk2ID[4];
           unsigned int Subchunk2Size;
     wav;
    FILE *original, *fast;
    original = fopen("Alejandro_project.wav", "rb");
    fast = fopen("Alejandro_fast.wav", "wb");
    if (original == NULL) 
                 printf("File does not exist.\n");
                 return 0;
    
    fread(&wav, 1, 44, original);
    unsigned short int data[12 * wav.SampleRate]
    int i;
    for (i = 0; i < Subchunk2Size / 2; i++)
        fread(&data[i], 1, 2, original);
    fwrite(&wav, 1, 44, fast);
    unsigned int fastSampleRate = wav.SampleRate * 2;
    unsigned int fastByteRate = 2 * fastSampleRate;
    fseek(fast, 24, SEEK_SET);
    fwrite(&fastSampleRate, 4, 1, fast);
    fseek(fast, 28, SEEK_SET);
    fwrite(&fastByteRate, 4, 1, fast);
    fwrite(data, 1, 2, original);
    fclose(fast);
    fclose(original);

【问题讨论】：

您可能应该打包您的 WAVE 结构（#pragma pack(1) 或 __attribute__((__packed__)) 或其他）...它可能有不需要的填充。

程序启动时 Alejandro_fast.wav 是否已经包含该文件的副本？看起来您没有将标头之后的其余文件写入目标文件

@samgak 实际上，既然你提到了它，即使 Alejandro_fast.wav 确实 （最初）包含一个副本，它也会被丢弃，因为文件是用 " wb"...也许"r+b"会更好。

【参考方案1】：

有几个问题.. 对于初学者，您需要确保 WAVE 标头的结构已打包，以免结构内出现意外填充，从而导致某些字段未对齐并增加结构的大小.否则，您可能会在每个 unsigned short int 成员之后获得两个字节的额外填充。

#pragma pack(push,1) /* for VC, may also work for GCC */
struct WAVE 
     /* ...struct contents... */
 wav;
#pragma pack(pop)

其次，您似乎正试图简单地覆盖新文件中的 SampleRate 和 ByteRate 成员，而其余部分保持不变。这仅在新文件已经是旧文件的副本时才有效。如果是这样，您还需要将打开新文件的模式更改为“r+b”（读取模式+写入）而不是“wb”（写入模式），这样现有文件内容就不会被丢弃。

当您尝试写入标头时也会出错。这一行：

fread(original, 1, 44, fast);

应该是：

fwrite(&wav, 44, 1, fast);

将 44 个字节从 wav 写入新文件，而不是从新文件中读取并使用旧文件的 FILE * 作为目标。

---

如果新文件不是已经是旧文件的副本，您还需要复制文件的其余部分（包括标题的其他部分）。在这种情况下，这可能是最简单的（一旦打开文件）：

将旧文件的标头读入wav

fread(&wav, sizeof(wav), 1, original);

修改SampleRate 和ByteRate 字段

wav.SampleRate *= 2;
wav.ByteRate *= 2;

将整个修改后的wav标头写入新文件

fwrite(&wav, sizeof(wav), 1, fast);

循环复制旧文件的剩余部分到新文件中

char buf[1024];
int count;
while ((count = fread(buf, 1, sizeof(buf), original)) > 0)
    fwrite(buf, 1, count, fast);

..然后关闭文件并返回。

【参考方案2】：

我想通了。我删除了结构只是为了看看我在做什么。完成最终项目后，我将重新合并该结构。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() 
    FILE *original, *fast, *slow, *slowdown;
    unsigned int ChunkSize, Subchunk1Size, Subchunk2Size, RIFFSize, fmtSize, dataSize, SampleRate, ByteRate;
    unsigned short int AudioFormat, NumChannels, BlockAlign, BitsPerSample;
    char ChunkID[5], Format[5], Subchunk1ID[5], Subchunk2ID[5];
    ChunkID[4] = '\0';
    Format[4] = '\0';
    Subchunk1ID[4] = '\0';
    Subchunk2ID[4] = '\0';
    char path[FILENAME_MAX], dfast[FILENAME_MAX], dslow[FILENAME_MAX], dslowdown[FILENAME_MAX];
    printf("Enter path to Alejandro_project.wav file: ");
    scanf("%s", path);
    strcpy(dfast, path);
    dfast[strlen(path) - 21] = '\0';
    strcpy(dslow, dfast);
    strcpy(dslowdown, dslow);
    strcat(dfast, "Alejandro_fast.wav");
    strcat(dslow, "Alejandro_slow.wav");
    strcat(dslowdown, "Alejandro_slowdown.wav");
    original = fopen(path, "rb");
    if (!original) 
        printf("Error: file does not exist.\n");
        return EXIT_FAILURE;
    
    fread(ChunkID, 4, 1, original);
    fread(&ChunkSize, 4, 1, original);
    fread(Format, 4, 1, original);
    fread(Subchunk1ID, 4, 1, original);
    fread(&Subchunk1Size, 4, 1, original);
    fread(&AudioFormat, 2, 1, original);
    fread(&NumChannels, 2, 1, original);
    fread(&SampleRate, 4, 1, original);
    fread(&ByteRate, 4, 1, original);
    fread(&BlockAlign, 2, 1, original);
    fread(&BitsPerSample, 2, 1, original);
    fread(Subchunk2ID, 4, 1, original);
    fread(&Subchunk2Size, 4, 1, original);
    fmtSize = Subchunk1Size + 8;
    dataSize = Subchunk2Size + 8;
    RIFFSize = ChunkSize + 8 - (fmtSize + dataSize);
    printf("RIFF Size:     %d\n", RIFFSize);
    printf("fmt Size:      %d\n", fmtSize);
    printf("data Size:     %d\n\n", dataSize);
    printf("ChunkID:       %s\n", ChunkID);
    printf("ChunkSize:     %d\n", ChunkSize);
    printf("Format:        %s\n\n", Format);
    printf("Subchunk1ID:   %s\n", Subchunk1ID);
    printf("Subchunk1Size: %d\n", Subchunk1Size);
    printf("AudioFormat:   %d\n", AudioFormat);
    printf("NumChannels:   %d\n", NumChannels);
    printf("SampleRate:    %d\n", SampleRate);
    printf("ByteRate:      %d\n", ByteRate);
    printf("BlockAlign:    %d\n", BlockAlign);
    printf("BitsPerSample: %d\n\n", BitsPerSample);
    printf("Subchunk2ID:   %s\n", Subchunk2ID);
    printf("Subchunk2Size: %d\n", Subchunk2Size);
    fseek(original, 0, SEEK_SET);
    fast = fopen(dfast, "wb");
    unsigned int fastSampleRate = SampleRate * 2;
    unsigned int fastByteRate = 2 * fastSampleRate;
    fwrite(ChunkID, 4, 1, fast);
    fwrite(&ChunkSize, 4, 1, fast);
    fwrite(Format, 4, 1, fast);
    fwrite(Subchunk1ID, 4, 1, fast);
    fwrite(&Subchunk1Size, 4, 1, fast);
    fwrite(&AudioFormat, 2, 1, fast);
    fwrite(&NumChannels, 2, 1, fast);
    fwrite(&fastSampleRate, 4, 1, fast);
    fwrite(&fastByteRate, 4, 1, fast);
    fwrite(&BlockAlign, 2, 1, fast);
    fwrite(&BitsPerSample, 2, 1, fast);
    fwrite(Subchunk2ID, 4, 1, fast);
    fwrite(&Subchunk2Size, 4, 1, fast);
    short int data;
    unsigned int i;
    for (i = 0; i < Subchunk2Size / 2; i++) 
        fread(&data, 2, 1, original);
        fwrite(&data, 2, 1, fast);
    
    fclose(fast);
    fseek(original, 0, SEEK_SET);
    slow = fopen(dslow, "wb");
    unsigned int slowSampleRate = SampleRate / 2;
    unsigned int slowByteRate = 2 * slowSampleRate;
    fwrite(ChunkID, 4, 1, slow);
    fwrite(&ChunkSize, 4, 1, slow);
    fwrite(Format, 4, 1, slow);
    fwrite(Subchunk1ID, 4, 1, slow);
    fwrite(&Subchunk1Size, 4, 1, slow);
    fwrite(&AudioFormat, 2, 1, slow);
    fwrite(&NumChannels, 2, 1, slow);
    fwrite(&slowSampleRate, 4, 1, slow);
    fwrite(&slowByteRate, 4, 1, slow);
    fwrite(&BlockAlign, 2, 1, slow);
    fwrite(&BitsPerSample, 2, 1, slow);
    fwrite(Subchunk2ID, 4, 1, slow);
    fwrite(&Subchunk2Size, 4, 1, slow);
    for (i = 0; i < Subchunk2Size / 2; i++) 
        fread(&data, 2, 1, original);
        fwrite(&data, 2, 1, slow);
    
    fclose(slow);    
    fclose(original);
    system("pause");
    return EXIT_SUCCESS;

【参考方案3】：

要使速度加倍，您不能只更改 WAV 标头中的 sample rate 或 byte-rate。如果这样做，它会播放得很快，但由于音高错误而听起来很奇怪。相反，您需要使用适当的采样率转换 (SRC) 库将输入 WAV 文件转换为具有更快采样率的输出 WAV 文件。