Mercurial > sdl-ios-xcode
annotate docs/html/sdlaudiospec.html @ 3880:74e828c64315 SDL-1.2
Fixed bug #292
I might be on crack here.
It looks like SDL_ConvertMono() in src/audio/SDL_audiocvt.c adds the left and
right channels of a stereo stream together, and clamps the new mono channel if
it would overflow.
Shouldn't it be dividing by 2 to average the two sample points instead of
clamping? Otherwise the mono sample point's volume doubles in the conversion.
This would also make the conversion faster, as it replaces two branches per
sample frame with a bitwise shift.
--ryan.
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Sun, 24 Sep 2006 15:45:37 +0000 |
| parents | 355632dca928 |
| children |
| rev | line source |
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| 0 | 1 <HTML |
| 2 ><HEAD | |
| 3 ><TITLE | |
| 4 >SDL_AudioSpec</TITLE | |
| 5 ><META | |
| 6 NAME="GENERATOR" | |
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ |
| 0 | 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="Audio" | |
| 17 HREF="audio.html"><LINK | |
| 18 REL="NEXT" | |
| 19 TITLE="SDL_OpenAudio" | |
| 20 HREF="sdlopenaudio.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 | |
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31 SUMMARY="Header navigation table" |
| 0 | 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="audio.html" | |
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49 ACCESSKEY="P" |
| 0 | 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="sdlopenaudio.html" | |
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63 ACCESSKEY="N" |
| 0 | 64 >Next</A |
| 65 ></TD | |
| 66 ></TR | |
| 67 ></TABLE | |
| 68 ><HR | |
| 69 ALIGN="LEFT" | |
| 70 WIDTH="100%"></DIV | |
| 71 ><H1 | |
| 72 ><A | |
| 73 NAME="SDLAUDIOSPEC" | |
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74 ></A |
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75 >SDL_AudioSpec</H1 |
| 0 | 76 ><DIV |
| 77 CLASS="REFNAMEDIV" | |
| 78 ><A | |
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79 NAME="AEN6507" |
| 0 | 80 ></A |
| 81 ><H2 | |
| 82 >Name</H2 | |
| 83 >SDL_AudioSpec -- Audio Specification Structure</DIV | |
| 84 ><DIV | |
| 85 CLASS="REFSECT1" | |
| 86 ><A | |
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87 NAME="AEN6510" |
| 0 | 88 ></A |
| 89 ><H2 | |
| 90 >Structure Definition</H2 | |
| 91 ><PRE | |
| 92 CLASS="PROGRAMLISTING" | |
| 93 >typedef struct{ | |
| 94 int freq; | |
| 95 Uint16 format; | |
| 96 Uint8 channels; | |
| 97 Uint8 silence; | |
| 98 Uint16 samples; | |
| 99 Uint32 size; | |
| 100 void (*callback)(void *userdata, Uint8 *stream, int len); | |
| 101 void *userdata; | |
| 102 } SDL_AudioSpec;</PRE | |
| 103 ></DIV | |
| 104 ><DIV | |
| 105 CLASS="REFSECT1" | |
| 106 ><A | |
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107 NAME="AEN6513" |
| 0 | 108 ></A |
| 109 ><H2 | |
| 110 >Structure Data</H2 | |
| 111 ><DIV | |
| 112 CLASS="INFORMALTABLE" | |
| 113 ><A | |
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114 NAME="AEN6515" |
| 0 | 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 >freq</I | |
| 130 ></TT | |
| 131 ></TD | |
| 132 ><TD | |
| 133 ALIGN="LEFT" | |
| 134 VALIGN="TOP" | |
| 135 >Audio frequency in samples per second</TD | |
| 136 ></TR | |
| 137 ><TR | |
| 138 ><TD | |
| 139 ALIGN="LEFT" | |
| 140 VALIGN="TOP" | |
| 141 ><TT | |
| 142 CLASS="STRUCTFIELD" | |
| 143 ><I | |
| 144 >format</I | |
| 145 ></TT | |
| 146 ></TD | |
| 147 ><TD | |
| 148 ALIGN="LEFT" | |
| 149 VALIGN="TOP" | |
| 150 >Audio data format</TD | |
| 151 ></TR | |
| 152 ><TR | |
| 153 ><TD | |
| 154 ALIGN="LEFT" | |
| 155 VALIGN="TOP" | |
| 156 ><TT | |
| 157 CLASS="STRUCTFIELD" | |
| 158 ><I | |
| 159 >channels</I | |
| 160 ></TT | |
| 161 ></TD | |
| 162 ><TD | |
| 163 ALIGN="LEFT" | |
| 164 VALIGN="TOP" | |
| 165 >Number of channels: 1 mono, 2 stereo</TD | |
| 166 ></TR | |
| 167 ><TR | |
| 168 ><TD | |
| 169 ALIGN="LEFT" | |
| 170 VALIGN="TOP" | |
| 171 ><TT | |
| 172 CLASS="STRUCTFIELD" | |
| 173 ><I | |
| 174 >silence</I | |
| 175 ></TT | |
| 176 ></TD | |
| 177 ><TD | |
| 178 ALIGN="LEFT" | |
| 179 VALIGN="TOP" | |
| 180 >Audio buffer silence value (calculated)</TD | |
| 181 ></TR | |
| 182 ><TR | |
| 183 ><TD | |
| 184 ALIGN="LEFT" | |
| 185 VALIGN="TOP" | |
| 186 ><TT | |
| 187 CLASS="STRUCTFIELD" | |
| 188 ><I | |
| 189 >samples</I | |
| 190 ></TT | |
| 191 ></TD | |
| 192 ><TD | |
| 193 ALIGN="LEFT" | |
| 194 VALIGN="TOP" | |
| 195 >Audio buffer size in samples</TD | |
| 196 ></TR | |
| 197 ><TR | |
| 198 ><TD | |
| 199 ALIGN="LEFT" | |
| 200 VALIGN="TOP" | |
| 201 ><TT | |
| 202 CLASS="STRUCTFIELD" | |
| 203 ><I | |
| 204 >size</I | |
| 205 ></TT | |
| 206 ></TD | |
| 207 ><TD | |
| 208 ALIGN="LEFT" | |
| 209 VALIGN="TOP" | |
| 210 >Audio buffer size in bytes (calculated)</TD | |
| 211 ></TR | |
| 212 ><TR | |
| 213 ><TD | |
| 214 ALIGN="LEFT" | |
| 215 VALIGN="TOP" | |
| 216 ><TT | |
| 217 CLASS="STRUCTFIELD" | |
| 218 ><I | |
| 219 >callback(..)</I | |
| 220 ></TT | |
| 221 ></TD | |
| 222 ><TD | |
| 223 ALIGN="LEFT" | |
| 224 VALIGN="TOP" | |
| 225 >Callback function for filling the audio buffer</TD | |
| 226 ></TR | |
| 227 ><TR | |
| 228 ><TD | |
| 229 ALIGN="LEFT" | |
| 230 VALIGN="TOP" | |
| 231 ><TT | |
| 232 CLASS="STRUCTFIELD" | |
| 233 ><I | |
| 234 >userdata</I | |
| 235 ></TT | |
| 236 ></TD | |
| 237 ><TD | |
| 238 ALIGN="LEFT" | |
| 239 VALIGN="TOP" | |
| 240 >Pointer the user data which is passed to the callback function</TD | |
| 241 ></TR | |
| 242 ></TBODY | |
| 243 ></TABLE | |
| 244 ><P | |
| 245 ></P | |
| 246 ></DIV | |
| 247 ></DIV | |
| 248 ><DIV | |
| 249 CLASS="REFSECT1" | |
| 250 ><A | |
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251 NAME="AEN6550" |
| 0 | 252 ></A |
| 253 ><H2 | |
| 254 >Description</H2 | |
| 255 ><P | |
| 256 >The <SPAN | |
| 257 CLASS="STRUCTNAME" | |
| 258 >SDL_AudioSpec</SPAN | |
| 259 > structure is used to describe the format of some audio data. This structure is used by <A | |
| 260 HREF="sdlopenaudio.html" | |
| 261 ><TT | |
| 262 CLASS="FUNCTION" | |
| 263 >SDL_OpenAudio</TT | |
| 264 ></A | |
| 265 > and <A | |
| 266 HREF="sdlloadwav.html" | |
| 267 ><TT | |
| 268 CLASS="FUNCTION" | |
| 269 >SDL_LoadWAV</TT | |
| 270 ></A | |
| 271 >. While all fields are used by <TT | |
| 272 CLASS="FUNCTION" | |
| 273 >SDL_OpenAudio</TT | |
| 274 > only <TT | |
| 275 CLASS="STRUCTFIELD" | |
| 276 ><I | |
| 277 >freq</I | |
| 278 ></TT | |
| 279 >, <TT | |
| 280 CLASS="STRUCTFIELD" | |
| 281 ><I | |
| 282 >format</I | |
| 283 ></TT | |
| 284 >, <TT | |
| 285 CLASS="STRUCTFIELD" | |
| 286 ><I | |
| 287 >samples</I | |
| 288 ></TT | |
| 289 > and <TT | |
| 290 CLASS="STRUCTFIELD" | |
| 291 ><I | |
| 292 >channels</I | |
| 293 ></TT | |
| 294 > are used by <TT | |
| 295 CLASS="FUNCTION" | |
| 296 >SDL_LoadWAV</TT | |
| 297 >. We will detail these common members here.</P | |
| 298 ><DIV | |
| 299 CLASS="INFORMALTABLE" | |
| 300 ><A | |
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301 NAME="AEN6564" |
| 0 | 302 ></A |
| 303 ><P | |
| 304 ></P | |
| 305 ><TABLE | |
| 306 BORDER="0" | |
| 307 CLASS="CALSTABLE" | |
| 308 ><TBODY | |
| 309 ><TR | |
| 310 ><TD | |
| 311 ALIGN="LEFT" | |
| 312 VALIGN="TOP" | |
| 313 ><TT | |
| 314 CLASS="STRUCTFIELD" | |
| 315 ><I | |
| 316 >freq</I | |
| 317 ></TT | |
| 318 ></TD | |
| 319 ><TD | |
| 320 ALIGN="LEFT" | |
| 321 VALIGN="TOP" | |
| 322 ><P | |
| 323 >The number of samples sent to the sound device every second. Common values are 11025, 22050 and 44100. The higher the better.</P | |
| 324 ></TD | |
| 325 ></TR | |
| 326 ><TR | |
| 327 ><TD | |
| 328 ALIGN="LEFT" | |
| 329 VALIGN="TOP" | |
| 330 ><TT | |
| 331 CLASS="STRUCTFIELD" | |
| 332 ><I | |
| 333 >format</I | |
| 334 ></TT | |
| 335 ></TD | |
| 336 ><TD | |
| 337 ALIGN="LEFT" | |
| 338 VALIGN="TOP" | |
| 339 ><P | |
| 340 >Specifies the size and type of each sample element | |
| 341 <P | |
| 342 ></P | |
| 343 ><DIV | |
| 344 CLASS="VARIABLELIST" | |
| 345 ><DL | |
| 346 ><DT | |
| 347 ><TT | |
| 348 CLASS="LITERAL" | |
| 349 >AUDIO_U8</TT | |
| 350 ></DT | |
| 351 ><DD | |
| 352 ><P | |
| 353 >Unsigned 8-bit samples</P | |
| 354 ></DD | |
| 355 ><DT | |
| 356 ><TT | |
| 357 CLASS="LITERAL" | |
| 358 >AUDIO_S8</TT | |
| 359 ></DT | |
| 360 ><DD | |
| 361 ><P | |
| 362 >Signed 8-bit samples</P | |
| 363 ></DD | |
| 364 ><DT | |
| 365 ><TT | |
| 366 CLASS="LITERAL" | |
| 367 >AUDIO_U16</TT | |
| 368 > or <TT | |
| 369 CLASS="LITERAL" | |
| 370 >AUDIO_U16LSB</TT | |
| 371 ></DT | |
| 372 ><DD | |
| 373 ><P | |
| 374 >Unsigned 16-bit little-endian samples</P | |
| 375 ></DD | |
| 376 ><DT | |
| 377 ><TT | |
| 378 CLASS="LITERAL" | |
| 379 >AUDIO_S16</TT | |
| 380 > or <TT | |
| 381 CLASS="LITERAL" | |
| 382 >AUDIO_S16LSB</TT | |
| 383 ></DT | |
| 384 ><DD | |
| 385 ><P | |
| 386 >Signed 16-bit little-endian samples</P | |
| 387 ></DD | |
| 388 ><DT | |
| 389 ><TT | |
| 390 CLASS="LITERAL" | |
| 391 >AUDIO_U16MSB</TT | |
| 392 ></DT | |
| 393 ><DD | |
| 394 ><P | |
| 395 >Unsigned 16-bit big-endian samples</P | |
| 396 ></DD | |
| 397 ><DT | |
| 398 ><TT | |
| 399 CLASS="LITERAL" | |
| 400 >AUDIO_S16MSB</TT | |
| 401 ></DT | |
| 402 ><DD | |
| 403 ><P | |
| 404 >Signed 16-bit big-endian samples</P | |
| 405 ></DD | |
| 406 ><DT | |
| 407 ><TT | |
| 408 CLASS="LITERAL" | |
| 409 >AUDIO_U16SYS</TT | |
| 410 ></DT | |
| 411 ><DD | |
| 412 ><P | |
| 413 >Either <TT | |
| 414 CLASS="LITERAL" | |
| 415 >AUDIO_U16LSB</TT | |
| 416 > or <TT | |
| 417 CLASS="LITERAL" | |
| 418 >AUDIO_U16MSB</TT | |
| 419 > depending on you systems endianness</P | |
| 420 ></DD | |
| 421 ><DT | |
| 422 ><TT | |
| 423 CLASS="LITERAL" | |
| 424 >AUDIO_S16SYS</TT | |
| 425 ></DT | |
| 426 ><DD | |
| 427 ><P | |
| 428 >Either <TT | |
| 429 CLASS="LITERAL" | |
| 430 >AUDIO_S16LSB</TT | |
| 431 > or <TT | |
| 432 CLASS="LITERAL" | |
| 433 >AUDIO_S16MSB</TT | |
| 434 > depending on you systems endianness</P | |
| 435 ></DD | |
| 436 ></DL | |
| 437 ></DIV | |
| 438 ></P | |
| 439 ></TD | |
| 440 ></TR | |
| 441 ><TR | |
| 442 ><TD | |
| 443 ALIGN="LEFT" | |
| 444 VALIGN="TOP" | |
| 445 ><TT | |
| 446 CLASS="STRUCTFIELD" | |
| 447 ><I | |
| 448 >channels</I | |
| 449 ></TT | |
| 450 ></TD | |
| 451 ><TD | |
| 452 ALIGN="LEFT" | |
| 453 VALIGN="TOP" | |
| 454 >The number of seperate sound channels. 1 is mono (single channel), 2 is stereo (dual channel).</TD | |
| 455 ></TR | |
| 456 ><TR | |
| 457 ><TD | |
| 458 ALIGN="LEFT" | |
| 459 VALIGN="TOP" | |
| 460 ><TT | |
| 461 CLASS="STRUCTFIELD" | |
| 462 ><I | |
| 463 >samples</I | |
| 464 ></TT | |
| 465 ></TD | |
| 466 ><TD | |
| 467 ALIGN="LEFT" | |
| 468 VALIGN="TOP" | |
| 469 >When used with <A | |
| 470 HREF="sdlopenaudio.html" | |
| 471 ><TT | |
| 472 CLASS="FUNCTION" | |
| 473 >SDL_OpenAudio</TT | |
| 474 ></A | |
| 475 > this refers to the size of the audio buffer in samples. A sample a chunk of audio data of the size specified in <TT | |
| 476 CLASS="PARAMETER" | |
| 477 ><I | |
| 478 >format</I | |
| 479 ></TT | |
| 480 > mulitplied by the number of channels. When the <SPAN | |
| 481 CLASS="STRUCTNAME" | |
| 482 >SDL_AudioSpec</SPAN | |
| 483 > is used with <A | |
| 484 HREF="sdlloadwav.html" | |
| 485 ><TT | |
| 486 CLASS="FUNCTION" | |
| 487 >SDL_LoadWAV</TT | |
| 488 ></A | |
| 489 > <TT | |
| 490 CLASS="STRUCTFIELD" | |
| 491 ><I | |
| 492 >samples</I | |
| 493 ></TT | |
| 494 > is set to 4096.</TD | |
| 495 ></TR | |
| 496 ></TBODY | |
| 497 ></TABLE | |
| 498 ><P | |
| 499 ></P | |
| 500 ></DIV | |
| 501 ></DIV | |
| 502 ><DIV | |
| 503 CLASS="REFSECT1" | |
| 504 ><A | |
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505 NAME="AEN6639" |
| 0 | 506 ></A |
| 507 ><H2 | |
| 508 >See Also</H2 | |
| 509 ><P | |
| 510 ><A | |
| 511 HREF="sdlopenaudio.html" | |
| 512 ><TT | |
| 513 CLASS="FUNCTION" | |
| 514 >SDL_OpenAudio</TT | |
| 515 ></A | |
| 516 >, | |
| 517 <A | |
| 518 HREF="sdlloadwav.html" | |
| 519 ><TT | |
| 520 CLASS="FUNCTION" | |
| 521 >SDL_LoadWAV</TT | |
| 522 ></A | |
| 523 ></P | |
| 524 ></DIV | |
| 525 ><DIV | |
| 526 CLASS="NAVFOOTER" | |
| 527 ><HR | |
| 528 ALIGN="LEFT" | |
| 529 WIDTH="100%"><TABLE | |
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530 SUMMARY="Footer navigation table" |
| 0 | 531 WIDTH="100%" |
| 532 BORDER="0" | |
| 533 CELLPADDING="0" | |
| 534 CELLSPACING="0" | |
| 535 ><TR | |
| 536 ><TD | |
| 537 WIDTH="33%" | |
| 538 ALIGN="left" | |
| 539 VALIGN="top" | |
| 540 ><A | |
| 541 HREF="audio.html" | |
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542 ACCESSKEY="P" |
| 0 | 543 >Prev</A |
| 544 ></TD | |
| 545 ><TD | |
| 546 WIDTH="34%" | |
| 547 ALIGN="center" | |
| 548 VALIGN="top" | |
| 549 ><A | |
| 550 HREF="index.html" | |
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551 ACCESSKEY="H" |
| 0 | 552 >Home</A |
| 553 ></TD | |
| 554 ><TD | |
| 555 WIDTH="33%" | |
| 556 ALIGN="right" | |
| 557 VALIGN="top" | |
| 558 ><A | |
| 559 HREF="sdlopenaudio.html" | |
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560 ACCESSKEY="N" |
| 0 | 561 >Next</A |
| 562 ></TD | |
| 563 ></TR | |
| 564 ><TR | |
| 565 ><TD | |
| 566 WIDTH="33%" | |
| 567 ALIGN="left" | |
| 568 VALIGN="top" | |
| 569 >Audio</TD | |
| 570 ><TD | |
| 571 WIDTH="34%" | |
| 572 ALIGN="center" | |
| 573 VALIGN="top" | |
| 574 ><A | |
| 575 HREF="audio.html" | |
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576 ACCESSKEY="U" |
| 0 | 577 >Up</A |
| 578 ></TD | |
| 579 ><TD | |
| 580 WIDTH="33%" | |
| 581 ALIGN="right" | |
| 582 VALIGN="top" | |
| 583 >SDL_OpenAudio</TD | |
| 584 ></TR | |
| 585 ></TABLE | |
| 586 ></DIV | |
| 587 ></BODY | |
| 588 ></HTML | |
| 589 > |