采样率转换的开源代码框架有resample、libresample、sndfile-resample、libresample4j等。

libresample andsndfile-resample (fromlibsamplerate) (in the Planet CCRMA Distribution).

• libsoxr, the SoX resampler library
• ssrc (from Shibatch)
• There is a project combining ssrc andsox
• New in 2016 is a Python (Cython) implementation:resampy
• Brick (onGithub).
• Smarc, available as a command-line program or C library.
• The resample software package contains free sampling-rate conversion and filter design utilities written in C.
  • Older Version for NeXT Computers.
  • Original 1983+ source for the PDP KL-10.
• Erik de Castro Lopo's "SecretRabbitCode" libsamplerate

• libresample based on `resample-1.7P

• libresample4j is a Java port oflibresample.

• Open Source Audio Library Project (OSALP) contains a C++ class based onresample.
• The Speex speech coder/decoder.
• More at another large list of implementations and their relative performance.
  文本重点介绍 libresample 的使用方法。
  转换器类型
  enum
  {
   SRC_SINC_BEST_QUALITY  = 0,
   SRC_SINC_MEDIUM_QUALITY  = 1,
   SRC_SINC_FASTEST   = 2,
   SRC_ZERO_ORDER_HOLD   = 3,//零阶采样和保持器
   SRC_LINEAR     = 4,//插值
  } ;
  //简单转换函数
  int src_simple (SRC_DATA *data, int converter_type, int channels) ;
  具体参考samplerate.h头文件。
• 调用实例：
• int convert2(unsigned char* bufferAAC, size_t buf_sizeAAC, unsigned char* bufferPCM, size_t & buf_sizePCM)
  {
   unsigned char* pcm_data = NULL;
   if (!m_bNeAACDecInit)
   {
    //initialize decoder
    NeAACDecInit(decoder, bufferAAC, buf_sizeAAC, &samplerate, &channels);
    printf("samplerate %d, channels %d\n", samplerate, channels);
    m_bNeAACDecInit = true;
   }
   //decode ADTS frame
   pcm_data = (unsigned char*)NeAACDecDecode(decoder, &frame_info, bufferAAC, buf_sizeAAC);

   if (frame_info.error > 0)
   {
    printf("%s\n", NeAACDecGetErrorMessage(frame_info.error));
    return -1;
   }
   else if (pcm_data && frame_info.samples > 0)
   {
    printf("frame info: bytesconsumed %d, channels %d, header_type %d\
               object_type %d, samples %d, samplerate %d\n",
            frame_info.bytesconsumed,
            frame_info.channels, frame_info.header_type,
            frame_info.object_type, frame_info.samples,
            frame_info.samplerate);

    buf_sizePCM = frame_info.samples * frame_info.channels;
    memcpy(bufferPCM,pcm_data,buf_sizePCM);
    //采样率变成8000HZ
    float in[4096] = { 0 };
    float out[4096] = { 0 };
    int j = 0;
    for (j = 0; j < 4096 && j < buf_sizePCM; j++)
    {
     in[j] = pcm_data[j];
    }
    SRC_DATA dataResample;
    dataResample.data_in = in;
    dataResample.data_out = out;
    dataResample.input_frames = frame_info.samples;
    dataResample.output_frames = frame_info.samples;
    dataResample.src_ratio =  8000.0/frame_info.samplerate;
  int nRetResample = 0;
  //在测试过程中发现，如果是frame_info.samplerate%8000是非整数倍，用SRC_LINEAR方法转换采样率的话，效果很差。
  if(frame_info.samplerate%8000 == 0)
  {
  nRetResample = src_simple(&dataResample,SRC_LINEAR, frame_info.channels);
  }
  else
  {
  nRetResample = src_simple(&dataResample,SRC_ZERO_ORDER_HOLD, frame_info.channels);
  }
  
    /*
    buf_sizePCM = dataResample.output_frames_gen * frame_info.channels;
    for (j = 0; j < 4096 && j < buf_sizePCM; j++)
    {
     bufferPCM[j] = Float2UChar(dataResample.data_out[j]);
    }
    */
    //声道变成单声道
    buf_sizePCM = dataResample.output_frames_gen * frame_info.channels;
    if(frame_info.channels == 2)
    {
     //从双声道的数据中提取单通道 
     int i = 0;
     for (i = 0, j = 0; i<4096 && i<buf_sizePCM && j<2048; i += 4, j += 2)
     {
      bufferPCM[j] = Float2UChar(out[i]);
      bufferPCM[j + 1] = Float2UChar(out[i + 1]);
     }
     buf_sizePCM = buf_sizePCM/2;
    }
    else
    {
     memcpy(bufferPCM,out,buf_sizePCM);
    }
    /*
    //声道变成单声道
    if(frame_info.channels == 2)
    {
     //从双声道的数据中提取单通道 
     for (int i = 0, j = 0; i<4096 && i<buf_sizePCM && j<2048; i += 4, j += 2)
     {
      bufferPCM[j] = pcm_data[i];
      bufferPCM[j + 1] = pcm_data[i + 1];
     }
     buf_sizePCM = buf_sizePCM/2;
     memcpy(bufferPCM,bufferPCM,buf_sizePCM);
    }
    else
    {
     memcpy(bufferPCM,pcm_data,buf_sizePCM);
    }
    */
    return 0;
   }

   return -1;
  }
  
  

  libsamplerate-vs2008下载地址： http://download.csdn.net/detail/byxdaz/9722122
• resample-1.7：http://www-ccrma.stanford.edu/~jos/resample/
• libsample：  https://github.com/minorninth/libresample
  
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