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7.1 KiB
HTML
548 lines
7.1 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>SDL_AudioCVT</TITLE
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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REL="HOME"
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TITLE="SDL Library Documentation"
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TITLE="Audio"
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HREF="sdlbuildaudiocvt.html"></HEAD
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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>SDL Library Documentation</TH
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WIDTH="10%"
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>Prev</A
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="sdlbuildaudiocvt.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
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><A
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NAME="SDLAUDIOCVT"
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>SDL_AudioCVT</A
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></H1
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><DIV
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CLASS="REFNAMEDIV"
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><A
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NAME="AEN6337"
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></A
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><H2
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>Name</H2
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>SDL_AudioCVT -- Audio Conversion Structure</DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN6340"
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></A
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><H2
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>Structure Definition</H2
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><PRE
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CLASS="PROGRAMLISTING"
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>typedef struct{
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int needed;
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Uint16 src_format;
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Uint16 dest_format;
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double rate_incr;
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Uint8 *buf;
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int len;
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int len_cvt;
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int len_mult;
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double len_ratio;
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void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
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int filter_index;
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} SDL_AudioCVT;</PRE
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN6343"
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></A
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><H2
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>Structure Data</H2
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><DIV
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CLASS="INFORMALTABLE"
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><A
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NAME="AEN6345"
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></A
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><P
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></P
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><TABLE
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BORDER="0"
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CLASS="CALSTABLE"
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><TBODY
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>needed</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Set to one if the conversion is possible</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>src_format</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Audio format of the source</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>dest_format</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Audio format of the destination</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>rate_incr</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Rate conversion increment</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>buf</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Audio buffer</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Length of the original audio buffer in bytes</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>len_cvt</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Length of converted audio buffer in bytes (calculated)</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>buf</I
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></TT
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> must be <TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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>*<TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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> bytes in size(calculated)</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>len_ratio</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Final audio size is <TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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>*<TT
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CLASS="STRUCTFIELD"
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><I
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>len_ratio</I
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></TT
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></TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>filters[10](..)</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Pointers to functions needed for this conversion</TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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><TT
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CLASS="STRUCTFIELD"
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><I
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>filter_index</I
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></TT
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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>Current conversion function</TD
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></TR
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></TBODY
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></TABLE
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><P
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></P
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></DIV
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN6397"
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></A
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><H2
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>Description</H2
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><P
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>The <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioCVT</SPAN
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> is used to convert audio data between different formats. A <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioCVT</SPAN
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> structure is created with the <A
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HREF="sdlbuildaudiocvt.html"
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><TT
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CLASS="FUNCTION"
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>SDL_BuildAudioCVT</TT
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></A
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> function, while the actual conversion is done by the <A
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HREF="sdlconvertaudio.html"
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><TT
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CLASS="FUNCTION"
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>SDL_ConvertAudio</TT
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></A
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> function.</P
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><P
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>Many of the fields in the <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioCVT</SPAN
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> structure should be considered private and their function will not be discussed here.</P
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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><SPAN
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CLASS="TYPE"
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>Uint8 *</SPAN
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><TT
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CLASS="STRUCTFIELD"
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><I
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>buf</I
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></TT
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></DT
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><DD
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><P
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>This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure <TT
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CLASS="STRUCTFIELD"
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><I
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>buf</I
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></TT
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> is large enough. See below.</P
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></DD
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><DT
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><SPAN
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CLASS="TYPE"
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>int</SPAN
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> <TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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></DT
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><DD
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><P
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>This is the length of the original audio data in bytes.</P
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></DD
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><DT
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><SPAN
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CLASS="TYPE"
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>int</SPAN
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> <TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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></DT
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><DD
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><P
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>As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of <TT
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CLASS="STRUCTFIELD"
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><I
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>buf</I
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></TT
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> should be <TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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>*<TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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>.</P
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></DD
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><DT
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><SPAN
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CLASS="TYPE"
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>double</SPAN
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> <TT
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CLASS="STRUCTFIELD"
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><I
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>len_ratio</I
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></TT
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></DT
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><DD
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><P
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>When you have finished converting your audio data, you need to know how much of your audio buffer is valid. <TT
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CLASS="STRUCTFIELD"
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><I
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>len</I
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></TT
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>*<TT
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CLASS="STRUCTFIELD"
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><I
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>len_ratio</I
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></TT
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> is the size of the converted audio data in bytes. This is very similar to <TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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>, however when the convert audio data is shorter than the original <TT
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CLASS="STRUCTFIELD"
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><I
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>len_mult</I
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></TT
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> would be 1. <TT
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CLASS="STRUCTFIELD"
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><I
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>len_ratio</I
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></TT
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>, on the other hand, would be a fractional number between 0 and 1.</P
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></DD
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></DL
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></DIV
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></DIV
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><DIV
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CLASS="REFSECT1"
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><A
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NAME="AEN6442"
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></A
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><H2
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>See Also</H2
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><P
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><A
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HREF="sdlbuildaudiocvt.html"
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><TT
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CLASS="FUNCTION"
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>SDL_BuildAudioCVT</TT
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></A
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>,
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<A
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HREF="sdlconvertaudio.html"
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><TT
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CLASS="FUNCTION"
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>SDL_ConvertAudio</TT
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></A
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>,
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<A
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HREF="sdlaudiospec.html"
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><SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioSpec</SPAN
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></A
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></P
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