正在从wavfile标头读取采样率

Reading samplerate from a wavfile header

本文关键字：读取 采样率 wavfile      更新时间：2023-10-16

我正在编写要在wave文件中读取的代码。

我以这份文件为指导。

它指定报头的字节22是波形文件的通道数，报头的字节24是采样率。

我使用的是Ableton输出的2通道16位44100hz的测试文件。我已经确认了测试波形文件的格式是大胆的，以确保它确实是44100hz采样率。

当我读取wave文件时，我得到的采样率值为-21436。我确信我的代码读取一个小的endian整数是正确的。我确信我的测试波形文件是正确的。所以现在我不知道为什么读取的采样率不正确。。。。

我的int读取代码如下。

int ReadInt(char* bytes , int start) { return (bytes[start+3] << 24) + (bytes[start+2] << 16) + (bytes[start+1] << 8) + bytes[start]; }

读取波形文件的函数如下。。。

WavFile::WavFile(std::string filename)
{
    std::ifstream ifs;      
    ifs.open( filename, std::ios::binary | std::ios::in );
    LogStream(LOG_DEBUG) << "WavFile::WavFile - - - - BEGIN READING WAV - - - -";
    if(ifs.fail())
        throw std::invalid_argument("WavFile::WavFile : Failed to open wavFile "+filename);
    char hbytes[HEADER_SIZE];
    ifs.read(hbytes , HEADER_SIZE);
    // check that this is actually a wave file
    bool valid_riff = hbytes[0]=='R' && hbytes[1]=='I' && hbytes[2]=='F' && hbytes[3]=='F';
    bool valid_wave = hbytes[8]=='W' && hbytes[9]=='A' && hbytes[10]=='V' && hbytes[11]=='E';
    bool valid_ftm = (hbytes[12]=='f' && hbytes[13]=='m' && hbytes[14]=='t' && hbytes[15]==' ');
    bool valid_data = (hbytes[36]=='d' && hbytes[37]=='a' && hbytes[38]=='t' && hbytes[39]=='a');
    LogStream(LOG_DEBUG) << "WavFile::WavFile - valid_riff="<<valid_riff<<" valid_wave="<<valid_wave<<" valid_ftm="<<valid_ftm<<" valid_data="<<valid_data;
    if(!(valid_data && valid_ftm && valid_riff))
        throw std::invalid_argument("WavFile::WavFile : Invalid argument - unable to open wavfile "+filename);
    int audioFormat = ReadShort(hbytes , 20);
    int SubChunk1Size = ReadInt(hbytes , 16);
    if(audioFormat != 1 || SubChunk1Size != 16)
        throw std::invalid_argument("WavFile::WavFile : Only uncompressed PCM wave format supported."+filename);    
    int subChunk2size = ReadInt(hbytes , 40);
    m_header.num_channels = ReadShort(hbytes , 22);
    m_header.sample_rate = ReadInt(hbytes , 24);
    m_header.bits_per_sample = ReadShort(hbytes , 34);
    LogStream(LOG_DEBUG) << "WavFile::WavFile num_channels="<<m_header.num_channels << " sample_rate="<<m_header.sample_rate<<" bits_per_sample="<<m_header.bits_per_sample;
    m_pcm_data.resize( subChunk2size / sizeof(int16_t) );
    LogStream(LOG_DEBUG) << "WavFile::WavFile - subChunk2size = "<<subChunk2size;
    LogStream(LOG_DEBUG) << "WavFile::WavFile - m_pcm_data.size() = "<<m_pcm_data.size();
    ifs.read((char*)m_pcm_data.data() , subChunk2size);
    LogStream(LOG_DEBUG) << "WavFile: ifstream failbit="<<ifs.fail()<<" badbit="<<ifs.bad()<<" goodbit="<<ifs.good();
    ifs.close();
    LogStream(LOG_DEBUG) << "WavFile::WavFile - - - - END READING WAV - - - -n";
    LogStream(LOG_DEBUG) << "WavFile::WavFile";
}

44100具有十六进制值44ac（无符号int16），-21436也具有十六进制数值44ac（有符号int16。您可以通过以下方式（输出44100）来避免这种情况：

int main()
{
    char bytes[4] = { 0x44, 0xac, 0x00, 0x00 };
    printf("%in", (((unsigned char)bytes[3]) << 24) | (((unsigned char)bytes[2]) << 16) | (((unsigned char)bytes[1]) << 8) | ((unsigned char)bytes[0]));
    return 0;
}

或者简单地读取为无符号字节-这将避免其他字段出现同样的问题：

int main()
{
    unsigned char bytes[4] = { 0x44, 0xac, 0x00, 0x00 };
    printf("%in", (bytes[3] << 24) | (bytes[2] << 16) | (bytes[1] << 8) | bytes[0]);
    return 0;
}
相关文章：