forked from KolibriOS/kolibrios
567 lines
9.3 KiB
HTML
567 lines
9.3 KiB
HTML
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<HTML
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><HEAD
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><TITLE
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>SDL_OpenAudio</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.64
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"><LINK
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REL="HOME"
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TITLE="SDL Library Documentation"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Audio"
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HREF="audio.html"><LINK
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REL="PREVIOUS"
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TITLE="SDL_AudioSpec"
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HREF="sdlaudiospec.html"><LINK
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REL="NEXT"
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TITLE="SDL_PauseAudio"
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HREF="sdlpauseaudio.html"></HEAD
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><BODY
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CLASS="REFENTRY"
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BGCOLOR="#FFF8DC"
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TEXT="#000000"
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LINK="#0000ee"
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VLINK="#551a8b"
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ALINK="#ff0000"
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><DIV
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CLASS="NAVHEADER"
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WIDTH="100%"
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CELLSPACING="0"
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><TH
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COLSPAN="3"
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ALIGN="center"
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>SDL Library Documentation</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="sdlaudiospec.html"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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></TD
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><TD
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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="sdlpauseaudio.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="SDLOPENAUDIO"
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>SDL_OpenAudio</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="AEN6103"
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></A
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><H2
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>Name</H2
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>SDL_OpenAudio -- Opens the audio device with the desired parameters.</DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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><A
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NAME="AEN6106"
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></A
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><H2
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>Synopsis</H2
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><DIV
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CLASS="FUNCSYNOPSIS"
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><A
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NAME="AEN6107"
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></A
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><P
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></P
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><PRE
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CLASS="FUNCSYNOPSISINFO"
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>#include "SDL.h"</PRE
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><P
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><CODE
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><CODE
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CLASS="FUNCDEF"
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>int <B
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CLASS="FSFUNC"
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>SDL_OpenAudio</B
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></CODE
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>(SDL_AudioSpec *desired, SDL_AudioSpec *obtained);</CODE
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></P
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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="AEN6113"
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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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>This function opens the audio device with the <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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> parameters, and
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returns 0 if successful, placing the actual hardware parameters in the
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structure pointed to by <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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>. If <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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> is NULL, the audio
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data passed to the callback function will be guaranteed to be in the
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requested format, and will be automatically converted to the hardware
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audio format if necessary. This function returns -1 if it failed
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to open the audio device, or couldn't set up the audio thread.</P
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><P
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>To open the audio device a <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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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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> must be created.
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<PRE
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CLASS="PROGRAMLISTING"
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>SDL_AudioSpec *desired;
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.
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.
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desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));</PRE
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>
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You must then fill this structure with your desired audio specifications.</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="STRUCTNAME"
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>desired</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>freq</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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>The desired audio frequency in samples-per-second.</P
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></DD
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><DT
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><SPAN
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CLASS="STRUCTNAME"
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>desired</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>format</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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>The desired audio format (see <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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></DD
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><DT
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><SPAN
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CLASS="STRUCTNAME"
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>desired</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>samples</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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>The desired size of the audio buffer in samples. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware. Good values seem to range between 512 and 8192 inclusive, depending on the application and CPU speed. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time. A stereo sample consists of both right and left channels in LR ordering. Note that the number of samples is directly related to time by the following formula: ms = (samples*1000)/freq</P
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></DD
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><DT
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><SPAN
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CLASS="STRUCTNAME"
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>desired</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>callback</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 should be set to a function that will be called when the audio device is ready for more data. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer. This function usually runs in a separate thread, and so you should protect data structures that it accesses by calling <A
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HREF="sdllockaudio.html"
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><TT
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CLASS="FUNCTION"
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>SDL_LockAudio</TT
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></A
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> and <A
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HREF="sdlunlockaudio.html"
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><TT
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CLASS="FUNCTION"
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>SDL_UnlockAudio</TT
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></A
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> in your code. The callback prototype is:
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<PRE
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CLASS="PROGRAMLISTING"
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>void callback(void *userdata, Uint8 *stream, int len);</PRE
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>
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<TT
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CLASS="PARAMETER"
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><I
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>userdata</I
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></TT
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> is the pointer stored in <TT
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CLASS="STRUCTFIELD"
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><I
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>userdata</I
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></TT
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> field of the <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioSpec</SPAN
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>. <TT
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CLASS="PARAMETER"
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><I
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>stream</I
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></TT
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> is a pointer to the audio buffer you want to fill with information and <TT
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CLASS="PARAMETER"
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><I
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>len</I
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></TT
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> is the length of the audio buffer in bytes.</P
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></DD
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><DT
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><SPAN
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CLASS="STRUCTNAME"
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>desired</SPAN
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>-><TT
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CLASS="STRUCTFIELD"
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><I
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>userdata</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 pointer is passed as the first parameter to the <TT
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CLASS="FUNCTION"
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>callback</TT
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> function.</P
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></DD
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></DL
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></DIV
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><P
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><TT
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CLASS="FUNCTION"
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>SDL_OpenAudio</TT
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> reads these fields from the <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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> <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioSpec</SPAN
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> structure pass to the function and attempts to find an audio configuration matching your <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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>. As mentioned above, if the <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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> parameter is <TT
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CLASS="LITERAL"
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>NULL</TT
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> then SDL with convert from your <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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> audio settings to the hardware settings as it plays.</P
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><P
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>If <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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> is <TT
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CLASS="LITERAL"
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>NULL</TT
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> then the <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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> <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioSpec</SPAN
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> is your working specification, otherwise the <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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> <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioSpec</SPAN
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> becomes the working specification and the <TT
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CLASS="PARAMETER"
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><I
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>desirec</I
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></TT
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> specification can be deleted. The data in the working specification is used when building <SPAN
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CLASS="STRUCTNAME"
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>SDL_AudioCVT</SPAN
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>'s for converting loaded data to the hardware format.</P
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><P
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><TT
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CLASS="FUNCTION"
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>SDL_OpenAudio</TT
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> calculates the <TT
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CLASS="STRUCTFIELD"
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><I
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>size</I
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></TT
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> and <TT
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CLASS="STRUCTFIELD"
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><I
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>silence</I
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></TT
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> fields for both the <TT
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CLASS="PARAMETER"
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><I
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>desired</I
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></TT
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> and <TT
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CLASS="PARAMETER"
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><I
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>obtained</I
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></TT
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> specifications. The <TT
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CLASS="STRUCTFIELD"
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><I
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>size</I
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></TT
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> field stores the total size of the audio buffer in bytes, while the <TT
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CLASS="STRUCTFIELD"
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><I
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>silence</I
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></TT
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> stores the value used to represent silence in the audio buffer</P
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><P
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>The audio device starts out playing <TT
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CLASS="STRUCTFIELD"
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><I
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>silence</I
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></TT
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> when it's opened, and should be enabled for playing by calling <A
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HREF="sdlpauseaudio.html"
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><TT
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CLASS="FUNCTION"
|
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>SDL_PauseAudio</TT
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>(<TT
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CLASS="PARAMETER"
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><I
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>0</I
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></TT
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>)</A
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> when you are ready for your audio <TT
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CLASS="STRUCTFIELD"
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><I
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>callback</I
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></TT
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> function to be called. Since the audio driver may modify the requested <TT
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CLASS="STRUCTFIELD"
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><I
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>size</I
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></TT
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> of the audio buffer, you should allocate any local mixing buffers after you open the audio device.</P
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|
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></DIV
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||
|
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><DIV
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||
|
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CLASS="REFSECT1"
|
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|
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><A
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||
|
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NAME="AEN6200"
|
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|
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></A
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><H2
|
||
|
|
>Examples</H2
|
||
|
|
><PRE
|
||
|
|
CLASS="PROGRAMLISTING"
|
||
|
|
>/* Prototype of our callback function */
|
||
|
|
void my_audio_callback(void *userdata, Uint8 *stream, int len);
|
||
|
|
|
||
|
|
/* Open the audio device */
|
||
|
|
SDL_AudioSpec *desired, *obtained;
|
||
|
|
SDL_AudioSpec *hardware_spec;
|
||
|
|
|
||
|
|
/* Allocate a desired SDL_AudioSpec */
|
||
|
|
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
|
||
|
|
|
||
|
|
/* Allocate space for the obtained SDL_AudioSpec */
|
||
|
|
obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
|
||
|
|
|
||
|
|
/* 22050Hz - FM Radio quality */
|
||
|
|
desired->freq=22050;
|
||
|
|
|
||
|
|
/* 16-bit signed audio */
|
||
|
|
desired->format=AUDIO_S16LSB;
|
||
|
|
|
||
|
|
/* Large audio buffer reduces risk of dropouts but increases response time */
|
||
|
|
desired->samples=8192;
|
||
|
|
|
||
|
|
/* Our callback function */
|
||
|
|
desired->callback=my_audio_callback;
|
||
|
|
|
||
|
|
desired->userdata=NULL;
|
||
|
|
|
||
|
|
/* Open the audio device */
|
||
|
|
if ( SDL_OpenAudio(desired, obtained) < 0 ){
|
||
|
|
fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
|
||
|
|
exit(-1);
|
||
|
|
}
|
||
|
|
/* desired spec is no longer needed */
|
||
|
|
free(desired);
|
||
|
|
hardware_spec=obtained;
|
||
|
|
.
|
||
|
|
.
|
||
|
|
/* Prepare callback for playing */
|
||
|
|
.
|
||
|
|
.
|
||
|
|
.
|
||
|
|
/* Start playing */
|
||
|
|
SDL_PauseAudio(0);</PRE
|
||
|
|
></DIV
|
||
|
|
><DIV
|
||
|
|
CLASS="REFSECT1"
|
||
|
|
><A
|
||
|
|
NAME="AEN6203"
|
||
|
|
></A
|
||
|
|
><H2
|
||
|
|
>See Also</H2
|
||
|
|
><P
|
||
|
|
><A
|
||
|
|
HREF="sdlaudiospec.html"
|
||
|
|
><TT
|
||
|
|
CLASS="FUNCTION"
|
||
|
|
>SDL_AudioSpec</TT
|
||
|
|
></A
|
||
|
|
>,
|
||
|
|
<A
|
||
|
|
HREF="sdllockaudio.html"
|
||
|
|
><TT
|
||
|
|
CLASS="FUNCTION"
|
||
|
|
>SDL_LockAudio</TT
|
||
|
|
></A
|
||
|
|
>,
|
||
|
|
<A
|
||
|
|
HREF="sdlunlockaudio.html"
|
||
|
|
><TT
|
||
|
|
CLASS="FUNCTION"
|
||
|
|
>SDL_UnlockAudio</TT
|
||
|
|
></A
|
||
|
|
>,
|
||
|
|
<A
|
||
|
|
HREF="sdlpauseaudio.html"
|
||
|
|
><TT
|
||
|
|
CLASS="FUNCTION"
|
||
|
|
>SDL_PauseAudio</TT
|
||
|
|
></A
|
||
|
|
></P
|
||
|
|
></DIV
|
||
|
|
><DIV
|
||
|
|
CLASS="NAVFOOTER"
|
||
|
|
><HR
|
||
|
|
ALIGN="LEFT"
|
||
|
|
WIDTH="100%"><TABLE
|
||
|
|
WIDTH="100%"
|
||
|
|
BORDER="0"
|
||
|
|
CELLPADDING="0"
|
||
|
|
CELLSPACING="0"
|
||
|
|
><TR
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="left"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="sdlaudiospec.html"
|
||
|
|
>Prev</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="34%"
|
||
|
|
ALIGN="center"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="index.html"
|
||
|
|
>Home</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="right"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="sdlpauseaudio.html"
|
||
|
|
>Next</A
|
||
|
|
></TD
|
||
|
|
></TR
|
||
|
|
><TR
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="left"
|
||
|
|
VALIGN="top"
|
||
|
|
>SDL_AudioSpec</TD
|
||
|
|
><TD
|
||
|
|
WIDTH="34%"
|
||
|
|
ALIGN="center"
|
||
|
|
VALIGN="top"
|
||
|
|
><A
|
||
|
|
HREF="audio.html"
|
||
|
|
>Up</A
|
||
|
|
></TD
|
||
|
|
><TD
|
||
|
|
WIDTH="33%"
|
||
|
|
ALIGN="right"
|
||
|
|
VALIGN="top"
|
||
|
|
>SDL_PauseAudio</TD
|
||
|
|
></TR
|
||
|
|
></TABLE
|
||
|
|
></DIV
|
||
|
|
></BODY
|
||
|
|
></HTML
|
||
|
|
>
|