+
+
Callback API
+
+The callback API consists of the following functions :
+
+
+ typedef long (*src_callback_t) (void *cb_data, float **data) ;
+
+ SRC_STATE* src_callback_new (src_callback_t func,
+ int converter_type, int channels,
+ int *error, void* cb_data) ;
+
+ SRC_STATE* src_delete (SRC_STATE *state) ;
+
+ long src_callback_read (SRC_STATE *state, double src_ratio,
+ long frames, float *data) ;
+
+ int src_reset (SRC_STATE *state) ;
+ int src_set_ratio (SRC_STATE *state, double new_ratio) ;
+
+
+
+
+Like the
+ simple API
+and the
+ full API,
+the callback based API is able to operate on interleaved multi channel data.
+
+
+
+An example of the use of the callback based API can be found in the
+varispeed-play program in the examples/ directory of the
+source code tarball.
+
+
+
+
+
Initialisation
+
+ SRC_STATE* src_callback_new (src_callback_t func,
+ int converter_type, int channels,
+ int *error, void* cb_data) ;
+
+
+The src_callback_new function returns an anonymous pointer to a
+sample rate converter callback object, src_state.
+This is the same type of object as that returned by
+src_new, but with different internal state.
+Although these are the same object type, they cannot be used interchangeably.
+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 caller then passes the SRC_STATE object to the src_callback_read
+function to pull data out of the converter.
+When the caller is finished with the converter they should pass it to the
+clean up function src_delete.
+
+
+The func parameter is a user supplied function which must match the
+src_callback_t type signature while cb_data is a pointer to
+data which be passed as the first parameter to the user supplied callback
+function.
+This function is called by the converter whenever it needs input data as a
+result of being calls to src_callback_read.
+
+
+If the converter was initialised to work with more than one channel, the
+callback function must work with mutiple channels of interleaved data.
+The callback function should return the number of frames it supplying to
+the converter.
+For multi channel files, this return value should be the number of floats
+divided by the number of channels.
+
+
+The converter must be one of the supplied converter types documented
+here.
+
+
+The caller then passes the SRC_STATE pointer to the src_callback_read
+function to pull data out of the converter.
+
+
+
+
+
Callback Read
+
+ long src_callback_read (SRC_STATE *state, double src_ratio,
+ long frames, float *data) ;
+
+
+The src_callback_read function is passed the
+ SRC_STATE
+pointer returned by src_callback_new, the coversion ratio
+(output_sample_rate / input_sample_rate), the maximum number of output frames
+to generate and a pointer to a buffer in which to place the output data.
+For multi channel files, the data int the output buffer is stored in
+interleaved format.
+
+
+The src_callback_read function returns the number of frames generated
+or zero if an error occurs or it runs out of input (ie the user supplied
+callback function returns zero and there is no more data buffered internally).
+If an error has occurred, the function
+src_error will return non-zero.
+
+
+
+See also :
+ src_set_ratio
+
+
+
+
+
+