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Secret Rabbit Code (aka libsamplerate)
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<META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
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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>
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