docs/html/sdlconvertaudio.html

   1 <HTML
   2 ><HEAD
   3 ><TITLE
   4 >SDL_ConvertAudio</TITLE
   5 ><META
   6 NAME="GENERATOR"
   7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
   8 "><LINK
   9 REL="HOME"
  10 TITLE="SDL Library Documentation"
  11 HREF="index.html"><LINK
  12 REL="UP"
  13 TITLE="Audio"
  14 HREF="audio.html"><LINK
  15 REL="PREVIOUS"
  16 TITLE="SDL_BuildAudioCVT"
  17 HREF="sdlbuildaudiocvt.html"><LINK
  18 REL="NEXT"
  19 TITLE="SDL_MixAudio"
  20 HREF="sdlmixaudio.html"></HEAD
  21 ><BODY
  22 CLASS="REFENTRY"
  23 BGCOLOR="#FFF8DC"
  24 TEXT="#000000"
  25 LINK="#0000ee"
  26 VLINK="#551a8b"
  27 ALINK="#ff0000"
  28 ><DIV
  29 CLASS="NAVHEADER"
  30 ><TABLE
  31 SUMMARY="Header navigation table"
  32 WIDTH="100%"
  33 BORDER="0"
  34 CELLPADDING="0"
  35 CELLSPACING="0"
  36 ><TR
  37 ><TH
  38 COLSPAN="3"
  39 ALIGN="center"
  40 >SDL Library Documentation</TH
  41 ></TR
  42 ><TR
  43 ><TD
  44 WIDTH="10%"
  45 ALIGN="left"
  46 VALIGN="bottom"
  47 ><A
  48 HREF="sdlbuildaudiocvt.html"
  49 ACCESSKEY="P"
  50 >Prev</A
  51 ></TD
  52 ><TD
  53 WIDTH="80%"
  54 ALIGN="center"
  55 VALIGN="bottom"
  56 ></TD
  57 ><TD
  58 WIDTH="10%"
  59 ALIGN="right"
  60 VALIGN="bottom"
  61 ><A
  62 HREF="sdlmixaudio.html"
  63 ACCESSKEY="N"
  64 >Next</A
  65 ></TD
  66 ></TR
  67 ></TABLE
  68 ><HR
  69 ALIGN="LEFT"
  70 WIDTH="100%"></DIV
  71 ><H1
  72 ><A
  73 NAME="SDLCONVERTAUDIO"
  74 ></A
  75 >SDL_ConvertAudio</H1
  76 ><DIV
  77 CLASS="REFNAMEDIV"
  78 ><A
  79 NAME="AEN7048"
  80 ></A
  81 ><H2
  82 >Name</H2
  83 >SDL_ConvertAudio&nbsp;--&nbsp;Convert audio data to a desired audio format.</DIV
  84 ><DIV
  85 CLASS="REFSYNOPSISDIV"
  86 ><A
  87 NAME="AEN7051"
  88 ></A
  89 ><H2
  90 >Synopsis</H2
  91 ><DIV
  92 CLASS="FUNCSYNOPSIS"
  93 ><A
  94 NAME="AEN7052"
  95 ></A
  96 ><P
  97 ></P
  98 ><PRE
  99 CLASS="FUNCSYNOPSISINFO"
 100 >#include "SDL.h"</PRE
 101 ><P
 102 ><CODE
 103 ><CODE
 104 CLASS="FUNCDEF"
 105 >int <B
 106 CLASS="FSFUNC"
 107 >SDL_ConvertAudio</B
 108 ></CODE
 109 >(SDL_AudioCVT *cvt);</CODE
 110 ></P
 111 ><P
 112 ></P
 113 ></DIV
 114 ></DIV
 115 ><DIV
 116 CLASS="REFSECT1"
 117 ><A
 118 NAME="AEN7058"
 119 ></A
 120 ><H2
 121 >Description</H2
 122 ><P
 123 ><TT
 124 CLASS="FUNCTION"
 125 >SDL_ConvertAudio</TT
 126 > takes one parameter, <TT
 127 CLASS="PARAMETER"
 128 ><I
 129 >cvt</I
 130 ></TT
 131 >, which was previously initilized. Initilizing a <A
 132 HREF="sdlaudiocvt.html"
 133 ><SPAN
 134 CLASS="STRUCTNAME"
 135 >SDL_AudioCVT</SPAN
 136 ></A
 137 > is a two step process. First of all, the structure must be passed to <A
 138 HREF="sdlbuildaudiocvt.html"
 139 ><TT
 140 CLASS="FUNCTION"
 141 >SDL_BuildAudioCVT</TT
 142 ></A
 143 > along with source and destination format parameters. Secondly, the <SPAN
 144 CLASS="STRUCTNAME"
 145 >cvt</SPAN
 146 >-&#62;<TT
 147 CLASS="STRUCTFIELD"
 148 ><I
 149 >buf</I
 150 ></TT
 151 > and <SPAN
 152 CLASS="STRUCTNAME"
 153 >cvt</SPAN
 154 >-&#62;<TT
 155 CLASS="STRUCTFIELD"
 156 ><I
 157 >len</I
 158 ></TT
 159 > fields must be setup. <SPAN
 160 CLASS="STRUCTNAME"
 161 >cvt</SPAN
 162 >-&#62;<TT
 163 CLASS="STRUCTFIELD"
 164 ><I
 165 >buf</I
 166 ></TT
 167 > should point to the audio data and <SPAN
 168 CLASS="STRUCTNAME"
 169 >cvt</SPAN
 170 >-&#62;<TT
 171 CLASS="STRUCTFIELD"
 172 ><I
 173 >len</I
 174 ></TT
 175 > should be set to the length of the audio data in bytes. Remember, the length of the buffer pointed to by <TT
 176 CLASS="STRUCTFIELD"
 177 ><I
 178 >buf</I
 179 ></TT
 180 > show be <TT
 181 CLASS="STRUCTFIELD"
 182 ><I
 183 >len</I
 184 ></TT
 185 >*<TT
 186 CLASS="STRUCTFIELD"
 187 ><I
 188 >len_mult</I
 189 ></TT
 190 > bytes in length.</P
 191 ><P
 192 >Once the <SPAN
 193 CLASS="STRUCTNAME"
 194 >SDL_AudioCVT</SPAN
 195 >structure is initilized then we can pass it to <TT
 196 CLASS="FUNCTION"
 197 >SDL_ConvertAudio</TT
 198 >, which will convert the audio data pointer to by <SPAN
 199 CLASS="STRUCTNAME"
 200 >cvt</SPAN
 201 >-&#62;<TT
 202 CLASS="STRUCTFIELD"
 203 ><I
 204 >buf</I
 205 ></TT
 206 >. If <TT
 207 CLASS="FUNCTION"
 208 >SDL_ConvertAudio</TT
 209 > returned <SPAN
 210 CLASS="RETURNVALUE"
 211 >0</SPAN
 212 > then the conversion was completed successfully, otherwise <SPAN
 213 CLASS="RETURNVALUE"
 214 >-1</SPAN
 215 > is returned.</P
 216 ><P
 217 >If the conversion completed successfully then the converted audio data can be read from <SPAN
 218 CLASS="STRUCTNAME"
 219 >cvt</SPAN
 220 >-&#62;<TT
 221 CLASS="STRUCTFIELD"
 222 ><I
 223 >buf</I
 224 ></TT
 225 >. The amount of valid, converted, audio data in the buffer is equal to <SPAN
 226 CLASS="STRUCTNAME"
 227 >cvt</SPAN
 228 >-&#62;<TT
 229 CLASS="STRUCTFIELD"
 230 ><I
 231 >len</I
 232 ></TT
 233 >*<TT
 234 CLASS="STRUCTFIELD"
 235 ><I
 236 >cvt</I
 237 ></TT
 238 >-&#62;<SPAN
 239 CLASS="STRUCTNAME"
 240 >len_ratio</SPAN
 241 >.</P
 242 ></DIV
 243 ><DIV
 244 CLASS="REFSECT1"
 245 ><A
 246 NAME="AEN7093"
 247 ></A
 248 ><H2
 249 >Examples</H2
 250 ><PRE
 251 CLASS="PROGRAMLISTING"
 252 >/* Converting some WAV data to hardware format */
 253 void my_audio_callback(void *userdata, Uint8 *stream, int len);
 254
 255 SDL_AudioSpec *desired, *obtained;
 256 SDL_AudioSpec wav_spec;
 257 SDL_AudioCVT  wav_cvt;
 258 Uint32 wav_len;
 259 Uint8 *wav_buf;
 260 int ret;
 261
 262 /* Allocated audio specs */
 263 desired = malloc(sizeof(SDL_AudioSpec));
 264 obtained = malloc(sizeof(SDL_AudioSpec));
 265
 266 /* Set desired format */
 267 desired-&#62;freq=22050;
 268 desired-&#62;format=AUDIO_S16LSB;
 269 desired-&#62;samples=8192;
 270 desired-&#62;callback=my_audio_callback;
 271 desired-&#62;userdata=NULL;
 272
 273 /* Open the audio device */
 274 if ( SDL_OpenAudio(desired, obtained) &#60; 0 ){
 275   fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
 276   exit(-1);
 277 }
 278
 279 free(desired);
 280
 281 /* Load the test.wav */
 282 if( SDL_LoadWAV("test.wav", &#38;wav_spec, &#38;wav_buf, &#38;wav_len) == NULL ){
 283   fprintf(stderr, "Could not open test.wav: %s\n", SDL_GetError());
 284   SDL_CloseAudio();
 285   free(obtained);
 286   exit(-1);
 287 }
 288
 289 /* Build AudioCVT */
 290 ret = SDL_BuildAudioCVT(&#38;wav_cvt,
 291                         wav_spec.format, wav_spec.channels, wav_spec.freq,
 292                         obtained-&#62;format, obtained-&#62;channels, obtained-&#62;freq);
 293
 294 /* Check that the convert was built */
 295 if(ret==-1){
 296   fprintf(stderr, "Couldn't build converter!\n");
 297   SDL_CloseAudio();
 298   free(obtained);
 299   SDL_FreeWAV(wav_buf);
 300 }
 301
 302 /* Setup for conversion */
 303 wav_cvt.buf = malloc(wav_len * wav_cvt.len_mult);
 304 wav_cvt.len = wav_len;
 305 memcpy(wav_cvt.buf, wav_buf, wav_len);
 306
 307 /* We can delete to original WAV data now */
 308 SDL_FreeWAV(wav_buf);
 309
 310 /* And now we're ready to convert */
 311 SDL_ConvertAudio(&#38;wav_cvt);
 312
 313 /* do whatever */
 314 .
 315 .
 316 .
 317 .
 318 &#13;</PRE
 319 ></DIV
 320 ><DIV
 321 CLASS="REFSECT1"
 322 ><A
 323 NAME="AEN7096"
 324 ></A
 325 ><H2
 326 >See Also</H2
 327 ><P
 328 ><A
 329 HREF="sdlbuildaudiocvt.html"
 330 ><TT
 331 CLASS="FUNCTION"
 332 >SDL_BuildAudioCVT</TT
 333 ></A
 334 >,
 335 <A
 336 HREF="sdlaudiocvt.html"
 337 ><TT
 338 CLASS="FUNCTION"
 339 >SDL_AudioCVT</TT
 340 ></A
 341 ></P
 342 ></DIV
 343 ><DIV
 344 CLASS="NAVFOOTER"
 345 ><HR
 346 ALIGN="LEFT"
 347 WIDTH="100%"><TABLE
 348 SUMMARY="Footer navigation table"
 349 WIDTH="100%"
 350 BORDER="0"
 351 CELLPADDING="0"
 352 CELLSPACING="0"
 353 ><TR
 354 ><TD
 355 WIDTH="33%"
 356 ALIGN="left"
 357 VALIGN="top"
 358 ><A
 359 HREF="sdlbuildaudiocvt.html"
 360 ACCESSKEY="P"
 361 >Prev</A
 362 ></TD
 363 ><TD
 364 WIDTH="34%"
 365 ALIGN="center"
 366 VALIGN="top"
 367 ><A
 368 HREF="index.html"
 369 ACCESSKEY="H"
 370 >Home</A
 371 ></TD
 372 ><TD
 373 WIDTH="33%"
 374 ALIGN="right"
 375 VALIGN="top"
 376 ><A
 377 HREF="sdlmixaudio.html"
 378 ACCESSKEY="N"
 379 >Next</A
 380 ></TD
 381 ></TR
 382 ><TR
 383 ><TD
 384 WIDTH="33%"
 385 ALIGN="left"
 386 VALIGN="top"
 387 >SDL_BuildAudioCVT</TD
 388 ><TD
 389 WIDTH="34%"
 390 ALIGN="center"
 391 VALIGN="top"
 392 ><A
 393 HREF="audio.html"
 394 ACCESSKEY="U"
 395 >Up</A
 396 ></TD
 397 ><TD
 398 WIDTH="33%"
 399 ALIGN="right"
 400 VALIGN="top"
 401 >SDL_MixAudio</TD
 402 ></TR
 403 ></TABLE
 404 ></DIV
 405 ></BODY
 406 ></HTML
 407 >