mirror of
https://github.com/cookiengineer/audacity
synced 2025-05-06 23:02:42 +02:00
172 lines
5.5 KiB
HTML
172 lines
5.5 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML>
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<HEAD>
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<TITLE>
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Secret Rabbit Code (aka libsamplerate)
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</TITLE>
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<META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
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<META NAME="Version" CONTENT="libsamplerate-0.1.7">
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<META NAME="Description" CONTENT="The Secret Rabbit Code Home Page">
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<META NAME="Keywords" CONTENT="libsamplerate sound resample audio dsp Linux">
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<LINK REL=StyleSheet HREF="SRC.css" TYPE="text/css" MEDIA="all">
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</HEAD>
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<BODY TEXT="#FFFFFF" BGCOLOR="#000000" LINK="#FB1465" VLINK="#FB1465" ALINK="#FB1465">
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<!-- pepper -->
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<CENTER>
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<IMG SRC="SRC.png" HEIGHT=100 WIDTH=760 ALT="SRC.png">
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</CENTER>
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<BR>
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<!-- pepper -->
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<TABLE ALIGN="center" WIDTH="98%">
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<TR>
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<TD VALIGN="top">
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<BR>
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<DIV CLASS="nav">
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<BR>
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<A HREF="index.html">Home</A><BR>
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<BR>
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<A HREF="api_simple.html">Simple API</A><BR>
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<A HREF="api_full.html">Full API</A><BR>
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<A HREF="api_callback.html">Callback API</A><BR>
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<A HREF="api_misc.html">Miscellaneous</A><BR>
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<A HREF="api_misc.html#ErrorReporting">Error Handling</A><BR>
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<BR>
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<DIV CLASS="block">
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Author :<BR>Erik de Castro Lopo
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<BR><BR>
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</DIV>
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<IMG SRC=
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"/cgi-bin/Count.cgi?ft=6|frgb=55;55;55|tr=0|md=6|dd=B|st=1|sh=1|df=src_api.dat"
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HEIGHT=30 WIDTH=100 ALT="counter.gif">
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</DIV>
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</TD>
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<!-- ######################################################################## -->
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<TD VALIGN="top">
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<DIV CLASS="block">
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<H1><B>Callback API</B></H1>
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<P>
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The callback API consists of the following functions :
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</P>
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<PRE>
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typedef long (*src_callback_t) (void *cb_data, float **data) ;
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SRC_STATE* <A HREF="#Init">src_callback_new</A> (src_callback_t func,
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int converter_type, int channels,
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int *error, void* cb_data) ;
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SRC_STATE* <A HREF="api_full.html#CleanUp">src_delete</A> (SRC_STATE *state) ;
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long <A HREF="#Read">src_callback_read</A> (SRC_STATE *state, double src_ratio,
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long frames, float *data) ;
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int <A HREF="api_full.html#Reset">src_reset</A> (SRC_STATE *state) ;
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int <A HREF="api_full.html#SetRatio">src_set_ratio</A> (SRC_STATE *state, double new_ratio) ;
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</PRE>
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<BR>
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<P>
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Like the
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<A HREF="api_simple.html">simple API</a>
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and the
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<A HREF="api_full.html">full API</a>,
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the callback based API is able to operate on interleaved multi channel data.
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</P>
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<P>
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An example of the use of the callback based API can be found in the
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<B>varispeed-play</B> program in the <B>examples/</B> directory of the
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source code tarball.
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</P>
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<A NAME="Init"></A>
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<H3><BR>Initialisation</H3>
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<PRE>
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SRC_STATE* src_callback_new (src_callback_t func,
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int converter_type, int channels,
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int *error, void* cb_data) ;
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</PRE>
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<P>
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The <B>src_callback_new</B> function returns an anonymous pointer to a
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sample rate converter callback object, src_state.
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This is the same type of object as that returned by <A HREF="api_full.html#init">
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src_new</A>, but with different internal state.
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Although these are the same object type, they cannot be used interchangeably.
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If an error occurs the function returns a NULL pointer and fills in the
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error value pointed to by the <B>error</B> pointer supplied by the caller.
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</P>
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<P>
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The caller then passes the SRC_STATE object to the <B>src_callback_read</B>
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function to pull data out of the converter.
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When the caller is finished with the converter they should pass it to the
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clean up function <A HREF="api_full.html#CleanUp">src_delete</A>.
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</P>
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<P>
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The <B>func</B> parameter is a user supplied function which must match the
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<B>src_callback_t</B> type signature while <B>cb_data</B> is a pointer to
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data which be passed as the first parameter to the user supplied callback
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function.
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This function is called by the converter whenever it needs input data as a
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result of being calls to <B>src_callback_read</B>.
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</P>
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<P>
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If the converter was initialised to work with more than one channel, the
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callback function must work with mutiple channels of interleaved data.
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The callback function should return the number of frames it supplying to
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the converter.
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For multi channel files, this return value should be the number of floats
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divided by the number of channels.
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</P>
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<P>
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The converter must be one of the supplied converter types documented
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<A HREF="api_misc.html#Converters">here</A>.
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</P>
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<P>
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The caller then passes the SRC_STATE pointer to the <B>src_callback_read</B>
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function to pull data out of the converter.
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</P>
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<!-- pepper -->
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<A NAME="Read"></A>
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<H3><BR>Callback Read</H3>
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<PRE>
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long src_callback_read (SRC_STATE *state, double src_ratio,
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long frames, float *data) ;
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</PRE>
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<P>
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The <B>src_callback_read</B> function is passed the
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<A HREF="api_misc.html#SRC_DATA"><B>SRC_STATE</B></A>
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pointer returned by <B>src_callback_new</B>, the coversion ratio
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(output_sample_rate / input_sample_rate), the maximum number of output frames
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to generate and a pointer to a buffer in which to place the output data.
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For multi channel files, the data int the output buffer is stored in
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interleaved format.
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</P>
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<P>
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The <B>src_callback_read</B> function returns the number of frames generated
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or zero if an error occurs or it runs out of input (ie the user supplied
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callback function returns zero and there is no more data buffered internally).
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If an error has occurred, the function <A HREF="api_misc.html#ErrorReporting">
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src_error</A> will return non-zero.
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</P>
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<!-- pepper -->
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</DIV>
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</TD></TR>
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</TABLE>
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</BODY>
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</HTML>
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