Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Secret Rabbit Code (aka libsamplerate) Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41: Chris@41:
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Chris@41: Home
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Chris@41: Simple API
Chris@41: Full API
Chris@41: Callback API
Chris@41: Miscellaneous
Chris@41: Error Handling
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Chris@41: Author :
Erik de Castro Lopo Chris@41: Chris@41:

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Callback API

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Chris@41: The callback API consists of the following functions : Chris@41:

Chris@41: 
Chris@41:       typedef long (*src_callback_t) (void *cb_data, float **data) ;
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Chris@41:       SRC_STATE* src_callback_new (src_callback_t func,
Chris@41: 	                      int converter_type, int channels,
Chris@41: 	                      int *error, void* cb_data) ;
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Chris@41:       SRC_STATE* src_delete (SRC_STATE *state) ;
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Chris@41:       long src_callback_read (SRC_STATE *state, double src_ratio,
Chris@41: 	                       long frames, float *data) ;
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Chris@41:       int src_reset (SRC_STATE *state) ;
Chris@41:       int src_set_ratio (SRC_STATE *state, double new_ratio) ;
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Chris@41: Like the Chris@41: simple API Chris@41: and the Chris@41: full API, Chris@41: the callback based API is able to operate on interleaved multi channel data. Chris@41:

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Chris@41: An example of the use of the callback based API can be found in the Chris@41: varispeed-play program in the examples/ directory of the Chris@41: source code tarball. Chris@41:

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Initialisation

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Chris@41:       SRC_STATE* src_callback_new (src_callback_t func,
Chris@41: 	                      int converter_type, int channels,
Chris@41: 	                      int *error, void* cb_data) ;
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Chris@41: The src_callback_new function returns an anonymous pointer to a Chris@41: sample rate converter callback object, src_state. Chris@41: This is the same type of object as that returned by Chris@41: src_new, but with different internal state. Chris@41: Although these are the same object type, they cannot be used interchangeably. Chris@41: If an error occurs the function returns a NULL pointer and fills in the Chris@41: error value pointed to by the error pointer supplied by the caller. Chris@41:

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Chris@41: The caller then passes the SRC_STATE object to the src_callback_read Chris@41: function to pull data out of the converter. Chris@41: When the caller is finished with the converter they should pass it to the Chris@41: clean up function src_delete. Chris@41:

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Chris@41: The func parameter is a user supplied function which must match the Chris@41: src_callback_t type signature while cb_data is a pointer to Chris@41: data which be passed as the first parameter to the user supplied callback Chris@41: function. Chris@41: This function is called by the converter whenever it needs input data as a Chris@41: result of being calls to src_callback_read. Chris@41:

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Chris@41: If the converter was initialised to work with more than one channel, the Chris@41: callback function must work with mutiple channels of interleaved data. Chris@41: The callback function should return the number of frames it supplying to Chris@41: the converter. Chris@41: For multi channel files, this return value should be the number of floats Chris@41: divided by the number of channels. Chris@41:

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Chris@41: The converter must be one of the supplied converter types documented Chris@41: here. Chris@41:

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Chris@41: The caller then passes the SRC_STATE pointer to the src_callback_read Chris@41: function to pull data out of the converter. Chris@41:

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Callback Read

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Chris@41:       long src_callback_read (SRC_STATE *state, double src_ratio,
Chris@41: 	                       long frames, float *data) ;
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Chris@41: The src_callback_read function is passed the Chris@41: SRC_STATE Chris@41: pointer returned by src_callback_new, the coversion ratio Chris@41: (output_sample_rate / input_sample_rate), the maximum number of output frames Chris@41: to generate and a pointer to a buffer in which to place the output data. Chris@41: For multi channel files, the data int the output buffer is stored in Chris@41: interleaved format. Chris@41:

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Chris@41: The src_callback_read function returns the number of frames generated Chris@41: or zero if an error occurs or it runs out of input (ie the user supplied Chris@41: callback function returns zero and there is no more data buffered internally). Chris@41: If an error has occurred, the function Chris@41: src_error will return non-zero. Chris@41:

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Chris@41: See also : Chris@41: src_set_ratio Chris@41:

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