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| Secret Rabbit Code (aka libsamplerate) |
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| <A HREF="index.html">Home</A><BR> |
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| <A HREF="api_simple.html">Simple API</A><BR> |
| <A HREF="api_full.html">Full API</A><BR> |
| <A HREF="api_callback.html">Callback API</A><BR> |
| <A HREF="api_misc.html">Miscellaneous</A><BR> |
| <A HREF="api_misc.html#ErrorReporting">Error Handling</A><BR> |
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| Author :<BR>Erik de Castro Lopo |
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| <H1><B>Callback API</B></H1> |
| <P> |
| The callback API consists of the following functions : |
| </P> |
| <PRE> |
| typedef long (*src_callback_t) (void *cb_data, float **data) ; |
| |
| SRC_STATE* <A HREF="#Init">src_callback_new</A> (src_callback_t func, |
| int converter_type, int channels, |
| int *error, void* cb_data) ; |
| |
| SRC_STATE* <A HREF="api_full.html#CleanUp">src_delete</A> (SRC_STATE *state) ; |
| |
| long <A HREF="#Read">src_callback_read</A> (SRC_STATE *state, double src_ratio, |
| long frames, float *data) ; |
| |
| int <A HREF="api_full.html#Reset">src_reset</A> (SRC_STATE *state) ; |
| int <A HREF="api_full.html#SetRatio">src_set_ratio</A> (SRC_STATE *state, double new_ratio) ; |
| </PRE> |
| <BR> |
| |
| <P> |
| Like the |
| <A HREF="api_simple.html">simple API</a> |
| and the |
| <A HREF="api_full.html">full API</a>, |
| the callback based API is able to operate on interleaved multi channel data. |
| </P> |
| |
| <P> |
| An example of the use of the callback based API can be found in the |
| <B>varispeed-play</B> program in the <B>examples/</B> directory of the |
| source code tarball. |
| </P> |
| |
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| <A NAME="Init"></A> |
| <H3><BR>Initialisation</H3> |
| <PRE> |
| SRC_STATE* src_callback_new (src_callback_t func, |
| int converter_type, int channels, |
| int *error, void* cb_data) ; |
| </PRE> |
| <P> |
| The <B>src_callback_new</B> 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 <A HREF="api_full.html#init"> |
| src_new</A>, 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 <B>error</B> pointer supplied by the caller. |
| </P> |
| <P> |
| The caller then passes the SRC_STATE object to the <B>src_callback_read</B> |
| 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 <A HREF="api_full.html#CleanUp">src_delete</A>. |
| </P> |
| <P> |
| The <B>func</B> parameter is a user supplied function which must match the |
| <B>src_callback_t</B> type signature while <B>cb_data</B> 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 <B>src_callback_read</B>. |
| </P> |
| <P> |
| 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. |
| </P> |
| <P> |
| The converter must be one of the supplied converter types documented |
| <A HREF="api_misc.html#Converters">here</A>. |
| </P> |
| <P> |
| The caller then passes the SRC_STATE pointer to the <B>src_callback_read</B> |
| function to pull data out of the converter. |
| </P> |
| |
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| <A NAME="Read"></A> |
| <H3><BR>Callback Read</H3> |
| <PRE> |
| long src_callback_read (SRC_STATE *state, double src_ratio, |
| long frames, float *data) ; |
| </PRE> |
| <P> |
| The <B>src_callback_read</B> function is passed the |
| <A HREF="api_misc.html#SRC_DATA"><B>SRC_STATE</B></A> |
| pointer returned by <B>src_callback_new</B>, 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. |
| </P> |
| <P> |
| The <B>src_callback_read</B> 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 <A HREF="api_misc.html#ErrorReporting"> |
| src_error</A> will return non-zero. |
| </P> |
| |
| <P> |
| See also : |
| <A HREF="api_full.html#SetRatio"><B>src_set_ratio</B></A> |
| </P> |
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