Full API

The full API consists of the following functions :

SRC_STATE* src_new (int converter_type, int channels, int *error) ;
SRC_STATE* src_delete (SRC_STATE *state) ;

int src_process (SRC_STATE *state, SRC_DATA *data) ;
int src_reset (SRC_STATE *state) ;
int src_set_ratio (SRC_STATE *state, double new_ratio) ;

Initialisation

SRC_STATE* src_new (int converter_type, int channels, int *error) ;

The src_new function returns an anonymous pointer to a sample rate converter object, src_state. If an error occurs the function returns a NULL pointer and fills in the error value pointed to by the error pointer supplied by the caller. The converter must be one of the supplied converter types documented here.

Cleanup

SRC_STATE* src_delete (SRC_STATE *state) ;

The src_delete function frees up all memory allocated for the given sample rate converter object and returns a NULL pointer. The caller is responsible for freeing any memory passed to the sample rate converter via the pointer to the SRC_DATA struct.

Process

int src_process (SRC_STATE *state, SRC_DATA *data) ;

The src_process function processes the data provided by the caller in an SRC_DATA struct using the sample rate converter object specified by the SRC_STATE pointer. When operating on streaming data, this function can be called over and over again, with each new call providing new input data and returning new output data.

The SRC_DATA struct passed as the second parameter to the src_process function has the following fields:

typedef struct
{   const float  *data_in;
    float *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.

end_of_input

Equal to 0 if more input data is available and 1 otherwise.

Note that the data_in and data_out arrays may not overlap. If they do, the library will return an error code.

When the src_process 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 consumed to generate the provided number of output frames.

The src_process function returns non-zero if an error occurs. The non-zero error return value can be decoded into a text string using the function documented here.

Reset

int src_reset (SRC_STATE *state) ;

The src_reset function resets the internal state of the sample rate converter object to the same state it had immediately after its creation using src_new. This should be called whenever a sample rate converter is to be used on two separate, unrelated pieces of audio.

Clone

SRC_STATE* src_clone (SRC_STATE *state, int *error) ;

The src_clone function creates a copy of the internal state of the sample rate converter object. The output of the next call to src_process will be identical for both the original and cloned state (given the same SRC_DATA input). This could be used to later resume sample rate conversion at a specific location in a stream with the same state, which may be useful in real-time applications.

If an error occurs the function returns a NULL pointer and fills in the error value pointed to by the error pointer supplied by the caller.

Set Ratio

int src_set_ratio (SRC_STATE *state, double new_ratio) ;

When using the src_process or src_callback_process APIs and updating the src_ratio field of the SRC_DATA struct, the library will try to smoothly transition between the conversion ratio of the last call and the conversion ratio of the current call.

If the user wants to bypass this smooth transition and achieve a step response in the conversion ratio, the src_set_ratio function can be used to set the starting conversion ratio of the next call to src_process or src_callback_process.

This function returns non-zero on error and the error return value can be decoded into a text string using the function documented here.