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  4. >Audio Examples</TITLE
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  39. >SDL Library Documentation</TH
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  54. >Chapter 4. Examples</TD
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  69. CLASS="SECT1"
  70. ><H1
  71. CLASS="SECT1"
  72. ><A
  73. NAME="GUIDEAUDIOEXAMPLES"
  74. >Audio Examples</A
  75. ></H1
  76. ><P
  77. ></P
  78. ><DIV
  79. CLASS="SECT2"
  80. ><H2
  81. CLASS="SECT2"
  82. ><A
  83. NAME="AEN415"
  84. >Opening the audio device</A
  85. ></H2
  86. ><P
  87. ><PRE
  88. CLASS="PROGRAMLISTING"
  89. >    SDL_AudioSpec wanted;
  90.     extern void fill_audio(void *udata, Uint8 *stream, int len);
  91.  
  92.     /* Set the audio format */
  93.     wanted.freq = 22050;
  94.     wanted.format = AUDIO_S16;
  95.     wanted.channels = 2;    /* 1 = mono, 2 = stereo */
  96.     wanted.samples = 1024;  /* Good low-latency value for callback */
  97.     wanted.callback = fill_audio;
  98.     wanted.userdata = NULL;
  99.  
  100.     /* Open the audio device, forcing the desired format */
  101.     if ( SDL_OpenAudio(&wanted, NULL) < 0 ) {
  102.         fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
  103.         return(-1);
  104.     }
  105.     return(0);</PRE
  106. ></P
  107. ></DIV
  108. ><DIV
  109. CLASS="SECT2"
  110. ><H2
  111. CLASS="SECT2"
  112. ><A
  113. NAME="AEN419"
  114. >Playing audio</A
  115. ></H2
  116. ><P
  117. ><PRE
  118. CLASS="PROGRAMLISTING"
  119. >    static Uint8 *audio_chunk;
  120.     static Uint32 audio_len;
  121.     static Uint8 *audio_pos;
  122.  
  123.     /* The audio function callback takes the following parameters:
  124.        stream:  A pointer to the audio buffer to be filled
  125.        len:     The length (in bytes) of the audio buffer
  126.     */
  127.     void fill_audio(void *udata, Uint8 *stream, int len)
  128.     {
  129.         /* Only play if we have data left */
  130.         if ( audio_len == 0 )
  131.             return;
  132.  
  133.         /* Mix as much data as possible */
  134.         len = ( len > audio_len ? audio_len : len );
  135.         SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME)
  136.         audio_pos += len;
  137.         audio_len -= len;
  138.     }
  139.  
  140.     /* Load the audio data ... */
  141.  
  142.     ;;;;;
  143.  
  144.     audio_pos = audio_chunk;
  145.  
  146.     /* Let the callback function play the audio chunk */
  147.     SDL_PauseAudio(0);
  148.  
  149.     /* Do some processing */
  150.  
  151.     ;;;;;
  152.  
  153.     /* Wait for sound to complete */
  154.     while ( audio_len > 0 ) {
  155.         SDL_Delay(100);         /* Sleep 1/10 second */
  156.     }
  157.     SDL_CloseAudio();</PRE
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