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Initial revision
author Sam Lantinga <slouken@lokigames.com>
date Thu, 26 Apr 2001 16:45:43 +0000
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children 55f1f1b3e27d
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1 <HTML
2 ><HEAD
3 ><TITLE
4 >SDL_AudioCVT</TITLE
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35 ><TR
36 ><TH
37 COLSPAN="3"
38 ALIGN="center"
39 >SDL Library Documentation</TH
40 ></TR
41 ><TR
42 ><TD
43 WIDTH="10%"
44 ALIGN="left"
45 VALIGN="bottom"
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47 HREF="sdlfreewav.html"
48 >Prev</A
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59 ><A
60 HREF="sdlbuildaudiocvt.html"
61 >Next</A
62 ></TD
63 ></TR
64 ></TABLE
65 ><HR
66 ALIGN="LEFT"
67 WIDTH="100%"></DIV
68 ><H1
69 ><A
70 NAME="SDLAUDIOCVT"
71 >SDL_AudioCVT</A
72 ></H1
73 ><DIV
74 CLASS="REFNAMEDIV"
75 ><A
76 NAME="AEN6262"
77 ></A
78 ><H2
79 >Name</H2
80 >SDL_AudioCVT&nbsp;--&nbsp;Audio Conversion Structure</DIV
81 ><DIV
82 CLASS="REFSECT1"
83 ><A
84 NAME="AEN6265"
85 ></A
86 ><H2
87 >Structure Definition</H2
88 ><PRE
89 CLASS="PROGRAMLISTING"
90 >typedef struct{
91 int needed;
92 Uint16 src_format;
93 Uint16 dest_format;
94 double rate_incr;
95 Uint8 *buf;
96 int len;
97 int len_cvt;
98 int len_mult;
99 double len_ratio;
100 void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
101 int filter_index;
102 } SDL_AudioCVT;</PRE
103 ></DIV
104 ><DIV
105 CLASS="REFSECT1"
106 ><A
107 NAME="AEN6268"
108 ></A
109 ><H2
110 >Structure Data</H2
111 ><DIV
112 CLASS="INFORMALTABLE"
113 ><A
114 NAME="AEN6270"
115 ></A
116 ><P
117 ></P
118 ><TABLE
119 BORDER="0"
120 CLASS="CALSTABLE"
121 ><TBODY
122 ><TR
123 ><TD
124 ALIGN="LEFT"
125 VALIGN="TOP"
126 ><TT
127 CLASS="STRUCTFIELD"
128 ><I
129 >needed</I
130 ></TT
131 ></TD
132 ><TD
133 ALIGN="LEFT"
134 VALIGN="TOP"
135 >Set to one if the conversion is possible</TD
136 ></TR
137 ><TR
138 ><TD
139 ALIGN="LEFT"
140 VALIGN="TOP"
141 ><TT
142 CLASS="STRUCTFIELD"
143 ><I
144 >src_format</I
145 ></TT
146 ></TD
147 ><TD
148 ALIGN="LEFT"
149 VALIGN="TOP"
150 >Audio format of the source</TD
151 ></TR
152 ><TR
153 ><TD
154 ALIGN="LEFT"
155 VALIGN="TOP"
156 ><TT
157 CLASS="STRUCTFIELD"
158 ><I
159 >dest_format</I
160 ></TT
161 ></TD
162 ><TD
163 ALIGN="LEFT"
164 VALIGN="TOP"
165 >Audio format of the destination</TD
166 ></TR
167 ><TR
168 ><TD
169 ALIGN="LEFT"
170 VALIGN="TOP"
171 ><TT
172 CLASS="STRUCTFIELD"
173 ><I
174 >rate_incr</I
175 ></TT
176 ></TD
177 ><TD
178 ALIGN="LEFT"
179 VALIGN="TOP"
180 >Rate conversion increment</TD
181 ></TR
182 ><TR
183 ><TD
184 ALIGN="LEFT"
185 VALIGN="TOP"
186 ><TT
187 CLASS="STRUCTFIELD"
188 ><I
189 >buf</I
190 ></TT
191 ></TD
192 ><TD
193 ALIGN="LEFT"
194 VALIGN="TOP"
195 >Audio buffer</TD
196 ></TR
197 ><TR
198 ><TD
199 ALIGN="LEFT"
200 VALIGN="TOP"
201 ><TT
202 CLASS="STRUCTFIELD"
203 ><I
204 >len</I
205 ></TT
206 ></TD
207 ><TD
208 ALIGN="LEFT"
209 VALIGN="TOP"
210 >Length of the original audio buffer in bytes</TD
211 ></TR
212 ><TR
213 ><TD
214 ALIGN="LEFT"
215 VALIGN="TOP"
216 ><TT
217 CLASS="STRUCTFIELD"
218 ><I
219 >len_cvt</I
220 ></TT
221 ></TD
222 ><TD
223 ALIGN="LEFT"
224 VALIGN="TOP"
225 >Length of converted audio buffer in bytes (calculated)</TD
226 ></TR
227 ><TR
228 ><TD
229 ALIGN="LEFT"
230 VALIGN="TOP"
231 ><TT
232 CLASS="STRUCTFIELD"
233 ><I
234 >len_mult</I
235 ></TT
236 ></TD
237 ><TD
238 ALIGN="LEFT"
239 VALIGN="TOP"
240 ><TT
241 CLASS="STRUCTFIELD"
242 ><I
243 >buf</I
244 ></TT
245 > must be <TT
246 CLASS="STRUCTFIELD"
247 ><I
248 >len</I
249 ></TT
250 >*<TT
251 CLASS="STRUCTFIELD"
252 ><I
253 >len_mult</I
254 ></TT
255 > bytes in size(calculated)</TD
256 ></TR
257 ><TR
258 ><TD
259 ALIGN="LEFT"
260 VALIGN="TOP"
261 ><TT
262 CLASS="STRUCTFIELD"
263 ><I
264 >len_ratio</I
265 ></TT
266 ></TD
267 ><TD
268 ALIGN="LEFT"
269 VALIGN="TOP"
270 >Final audio size is <TT
271 CLASS="STRUCTFIELD"
272 ><I
273 >len</I
274 ></TT
275 >*<TT
276 CLASS="STRUCTFIELD"
277 ><I
278 >len_ratio</I
279 ></TT
280 ></TD
281 ></TR
282 ><TR
283 ><TD
284 ALIGN="LEFT"
285 VALIGN="TOP"
286 ><TT
287 CLASS="STRUCTFIELD"
288 ><I
289 >filters[10](..)</I
290 ></TT
291 ></TD
292 ><TD
293 ALIGN="LEFT"
294 VALIGN="TOP"
295 >Pointers to functions needed for this conversion</TD
296 ></TR
297 ><TR
298 ><TD
299 ALIGN="LEFT"
300 VALIGN="TOP"
301 ><TT
302 CLASS="STRUCTFIELD"
303 ><I
304 >filter_index</I
305 ></TT
306 ></TD
307 ><TD
308 ALIGN="LEFT"
309 VALIGN="TOP"
310 >Current conversion function</TD
311 ></TR
312 ></TBODY
313 ></TABLE
314 ><P
315 ></P
316 ></DIV
317 ></DIV
318 ><DIV
319 CLASS="REFSECT1"
320 ><A
321 NAME="AEN6322"
322 ></A
323 ><H2
324 >Description</H2
325 ><P
326 >The <SPAN
327 CLASS="STRUCTNAME"
328 >SDL_AudioCVT</SPAN
329 > is used to convert audio data between different formats. A <SPAN
330 CLASS="STRUCTNAME"
331 >SDL_AudioCVT</SPAN
332 > structure is created with the <A
333 HREF="sdlbuildaudiocvt.html"
334 ><TT
335 CLASS="FUNCTION"
336 >SDL_BuildAudioCVT</TT
337 ></A
338 > function, while the actual conversion is done by the <A
339 HREF="sdlconvertaudio.html"
340 ><TT
341 CLASS="FUNCTION"
342 >SDL_ConvertAudio</TT
343 ></A
344 > function.</P
345 ><P
346 >Many of the fields in the <SPAN
347 CLASS="STRUCTNAME"
348 >SDL_AudioCVT</SPAN
349 > structure should be considered private and their function will not be discussed here.</P
350 ><P
351 ></P
352 ><DIV
353 CLASS="VARIABLELIST"
354 ><DL
355 ><DT
356 ><SPAN
357 CLASS="TYPE"
358 >Uint8 *</SPAN
359 ><TT
360 CLASS="STRUCTFIELD"
361 ><I
362 >buf</I
363 ></TT
364 ></DT
365 ><DD
366 ><P
367 >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
368 CLASS="STRUCTFIELD"
369 ><I
370 >buf</I
371 ></TT
372 > is large enough. See below.</P
373 ></DD
374 ><DT
375 ><SPAN
376 CLASS="TYPE"
377 >int</SPAN
378 > <TT
379 CLASS="STRUCTFIELD"
380 ><I
381 >len</I
382 ></TT
383 ></DT
384 ><DD
385 ><P
386 >This is the length of the original audio data in bytes.</P
387 ></DD
388 ><DT
389 ><SPAN
390 CLASS="TYPE"
391 >int</SPAN
392 > <TT
393 CLASS="STRUCTFIELD"
394 ><I
395 >len_mult</I
396 ></TT
397 ></DT
398 ><DD
399 ><P
400 >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
401 CLASS="STRUCTFIELD"
402 ><I
403 >buf</I
404 ></TT
405 > should be <TT
406 CLASS="STRUCTFIELD"
407 ><I
408 >len</I
409 ></TT
410 >*<TT
411 CLASS="STRUCTFIELD"
412 ><I
413 >len_mult</I
414 ></TT
415 >.</P
416 ></DD
417 ><DT
418 ><SPAN
419 CLASS="TYPE"
420 >double</SPAN
421 > <TT
422 CLASS="STRUCTFIELD"
423 ><I
424 >len_ratio</I
425 ></TT
426 ></DT
427 ><DD
428 ><P
429 >When you have finished converting your audio data, you need to know how much of your audio buffer is valid. <TT
430 CLASS="STRUCTFIELD"
431 ><I
432 >len</I
433 ></TT
434 >*<TT
435 CLASS="STRUCTFIELD"
436 ><I
437 >len_ratio</I
438 ></TT
439 > is the size of the converted audio data in bytes. This is very similar to <TT
440 CLASS="STRUCTFIELD"
441 ><I
442 >len_mult</I
443 ></TT
444 >, however when the convert audio data is shorter than the original <TT
445 CLASS="STRUCTFIELD"
446 ><I
447 >len_mult</I
448 ></TT
449 > would be 1. <TT
450 CLASS="STRUCTFIELD"
451 ><I
452 >len_ratio</I
453 ></TT
454 >, on the other hand, would be a fractional number between 0 and 1.</P
455 ></DD
456 ></DL
457 ></DIV
458 ></DIV
459 ><DIV
460 CLASS="REFSECT1"
461 ><A
462 NAME="AEN6367"
463 ></A
464 ><H2
465 >See Also</H2
466 ><P
467 ><A
468 HREF="sdlbuildaudiocvt.html"
469 ><TT
470 CLASS="FUNCTION"
471 >SDL_BuildAudioCVT</TT
472 ></A
473 >,
474 <A
475 HREF="sdlconvertaudio.html"
476 ><TT
477 CLASS="FUNCTION"
478 >SDL_ConvertAudio</TT
479 ></A
480 >,
481 <A
482 HREF="sdlaudiospec.html"
483 ><SPAN
484 CLASS="STRUCTNAME"
485 >SDL_AudioSpec</SPAN
486 ></A
487 ></P
488 ></DIV
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513 >Home</A
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519 ><A
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521 >Next</A
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