Secret Rabbit Code (aka libsamplerate)
Author: Erik de Castro Lopo (erikd AT mega-nerd DOT com)
Description: The Secret Rabbit Code Home Page
Keywords: libsamplerate sound resample audio dsp Linux

| # Simple API Important Note: The simple API is not designed to work on small chunks of a larger piece of audio. If you attempt to use it this way you are doing it wrong and will not get the results you want. For processing audio data in chunks you must use the full api or the callback based api. The simple API consists of a single function :
          int src_simple (SRC_DATA *data, int converter_type, int channels) ;
The use of this function rather than the more fully featured API requires the caller to know the total length of the input data before hand and that all input and output data can be held in the system's memory at once. It also assumes that there is a single constant ratio between input and output sample rates. Dealing with the easy stuff first, the converter_type parameter should be one of the values defined in samplerate.h and documented here while the channels parameter specifies the number of interleaved channels that the sample rate converter is being asked to process (number of input channels and output channels is always equal). There is no hard upper limit on the number of channels; it is limited purely by the amount of memory available. The first parameter to src_simple is a pointer to an SRC_DATA struct (more info here) defined as follows:
          typedef struct
          {   float  *data_in, *data_out ;

              long   input_frames, output_frames ;
              long   input_frames_used, output_frames_gen ;

              int    end_of_input ;

              double src_ratio ;
          } SRC_DATA ;
The fields of this struct which must be filled in by the caller are:
          data_in       : A pointer to the input data samples.
          input_frames  : The number of frames of data pointed to by data_in.
          data_out      : A pointer to the output data samples.
          output_frames : Maximum number of frames pointer to by data_out.
          src_ratio     : Equal to output_sample_rate / input_sample_rate.
When the src_simple function returns output_frames_gen will be set to the number of output frames generated and input_frames_used will be set to the number of input frames used to generate the provided number of output frames. The src_simple function returns a non-zero value when an error occurs. See here for how to convert the error value into a text string.