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| 6 | libsndfile : Frequently Asked Questions. |
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| 9 | <META NAME="Description" CONTENT="The libsndfile FAQ."> |
| 10 | <META NAME="Keywords" CONTENT="WAV AIFF AU libsndfile sound audio dsp Linux"> |
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| 16 | |
| 17 | <H1><B>libsndfile : Frequently Asked Questions.</B></H1> |
| 18 | <P> |
| 19 | <A HREF="#Q001">Q1 : Do you plan to support XYZ codec in libsndfile?</A><BR/> |
| 20 | <A HREF="#Q002">Q2 : In version 0 the SF_INFO struct had a pcmbitwidth field |
| 21 | but version 1 does not. Why?</A><BR/> |
| 22 | <A HREF="#Q003">Q3 : Compiling is really slow on MacOS X. Why?</A><BR/> |
| 23 | <A HREF="#Q004">Q4 : When trying to compile libsndfile on Solaris I get a "bad |
| 24 | substitution" error during linking. What can I do to fix this?</A><BR/> |
| 25 | <A HREF="#Q005">Q5 : Why doesn't libsndfile do interleaving/de-interleaving?</A><BR/> |
| 26 | <A HREF="#Q006">Q6 : What's the best format for storing temporary files?</A><BR/> |
| 27 | <A HREF="#Q007">Q7 : On Linux/Unix/MacOS X, what's the best way of detecting the |
| 28 | presence of libsndfile?</A><BR/> |
| 29 | <A HREF="#Q008">Q8 : But I just want a simple Makefile! What do I do?</A><BR/> |
| 30 | <A HREF="#Q009">Q9 : How about adding the ability to write/read sound files to/from |
| 31 | memory buffers?</A><BR/> |
| 32 | <A HREF="#Q010">Q10 : Reading a 16 bit PCM file as normalised floats and then |
| 33 | writing them back changes some sample values. Why?</A><BR/> |
| 34 | <A HREF="#Q011">Q11 : I'm having problems with u-law encoded WAV files generated by |
| 35 | libsndfile in Winamp. Why?</A><BR/> |
| 36 | <A HREF="#Q012">Q12 : I'm looking at sf_read*. What are items? What are frames?</A><BR/> |
| 37 | <A HREF="#Q013">Q13 : Why can't libsndfile open this Sound Designer II (SD2) |
| 38 | file?</A><BR/> |
| 39 | <A HREF="#Q014">Q14 : I'd like to statically link libsndfile to my closed source |
| 40 | application. Can I buy a license so that this is possible?</A><BR/> |
| 41 | <A HREF="#Q015">Q15 : My program is crashing during a call to a function in libsndfile. |
| 42 | Is this a bug in libsndfile?</A><BR/> |
| 43 | <A HREF="#Q016">Q16 : Will you accept a fix for compiling libsndfile with compiler X? |
| 44 | </A><BR/> |
| 45 | <A HREF="#Q017">Q17 : Can libsndfile read/write files from/to UNIX pipes? |
| 46 | </A><BR/> |
| 47 | <A HREF="#Q018">Q18 : Is it possible to build a Universal Binary on Mac OS X? |
| 48 | </A><BR/> |
| 49 | <A HREF="#Q019">Q19 : I have project files for Visual Studio / XCode / Whatever. Why |
| 50 | don't you distribute them with libsndfile? |
| 51 | </A><BR/> |
| 52 | <A HREF="#Q020">Q20 : Why doesn't libsndfile support MP3? Lots of other Open Source |
| 53 | projects support it! |
| 54 | </A><BR/> |
| 55 | <A HREF="#Q021">Q21 : How do I use libsndfile in a closed source or commercial program |
| 56 | and comply with the license? |
| 57 | </A><BR/> |
| 58 | <A HREF="#Q022">Q22 : What versions of windows does libsndfile work on? |
| 59 | </A><BR/> |
| 60 | <A HREF="#Q023">Q23 : I'm cross compiling libsndfile for another platform. How can I |
| 61 | run the test suite? |
| 62 | </A><BR/> |
| 63 | <HR> |
| 64 | |
| 65 | <!-- ========================================================================= --> |
| 66 | <A NAME="Q001"></A> |
| 67 | <H2><BR/><B>Q1 : Do you plan to support XYZ codec in libsndfile?</B></H2> |
| 68 | <P> |
| 69 | If source code for XYZ codec is available under a suitable license (LGPL, BSD, |
| 70 | MIT etc) then yes, I'd like to add it. |
| 71 | </P> |
| 72 | <P> |
| 73 | If suitable documentation is available on how to decode and encode the format |
| 74 | then maybe, depending on how much work is involved. |
| 75 | </P> |
| 76 | <P> |
| 77 | If XYZ is some proprietary codec where no source code or documentation is |
| 78 | available then no. |
| 79 | </P> |
| 80 | <P> |
| 81 | So if you want support for XYZ codec, first find existing source code or |
| 82 | documentation. |
| 83 | If you can't find either then the answer is no. |
| 84 | </P> |
| 85 | <!-- ========================================================================= --> |
| 86 | <A NAME="Q002"></A> |
| 87 | <H2><BR/><B>Q2 : In version 0 the SF_INFO struct had a pcmbitwidth field |
| 88 | but version 1 does not. Why?</B></H2> |
| 89 | <P> |
| 90 | This was dropped for a number of reasons: |
| 91 | </P> |
| 92 | <UL> |
| 93 | <LI> pcmbitwidth makes little sense on compressed or floating point formats |
| 94 | <LI> with the new API you really don't need to know it |
| 95 | </UL> |
| 96 | <P> |
| 97 | As documented |
| 98 | <A HREF="http://www.mega-nerd.com/libsndfile/api.html#note1">here</A> |
| 99 | there is now a well defined behaviour which ensures that no matter what the |
| 100 | bit width of the source file, the scaling always does something sensible. |
| 101 | This makes it safe to read 8, 16, 24 and 32 bit PCM files using sf_read_short() |
| 102 | and always have the optimal behaviour. |
| 103 | </P> |
| 104 | |
| 105 | <!-- ========================================================================= --> |
| 106 | <A NAME="Q003"></A> |
| 107 | <H2><BR/><B>Q3 : Compiling is really slow on MacOS X. Why?</B></H2> |
| 108 | <P> |
| 109 | When you configure and compile libsndfile, it uses the /bin/sh shell for a number |
| 110 | of tasks (ie configure script and libtool). |
| 111 | Older versions of OS X (10.2?) shipped a really crappy Bourne shell as /bin/sh |
| 112 | which resulted in <b>really</b> slow compiles. |
| 113 | Newer version of OS X ship GNU Bash as /bin/sh and this answer doesn't apply in that |
| 114 | case. |
| 115 | </P> |
| 116 | <P> |
| 117 | To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to |
| 118 | /bin/sh.old and make a symlink from /bin/sh to the bash shell. |
| 119 | Bash is designed to behave as a Bourne shell when is is called as /bin/sh. |
| 120 | </P> |
| 121 | <P> |
| 122 | When I did this on my iBook running MacOS X, compile times dropped from 13 minutes |
| 123 | to 3 minutes. |
| 124 | </P> |
| 125 | |
| 126 | <!-- ========================================================================= --> |
| 127 | <A NAME="Q004"></A> |
| 128 | <H2><BR/><B>Q4 : When trying to compile libsndfile on Solaris I get a "bad |
| 129 | substitution" error on linking. Why?</B></H2> |
| 130 | <P> |
| 131 | It seems that the Solaris Bourne shell disagrees with GNU libtool. |
| 132 | </P> |
| 133 | <P> |
| 134 | To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to |
| 135 | /bin/sh.old and make a symlink from /bin/sh to the bash shell. |
| 136 | Bash is designed to behave as a Bourne shell when is is called as /bin/sh. |
| 137 | </P> |
| 138 | |
| 139 | <!-- ========================================================================= --> |
| 140 | <A NAME="Q005"></A> |
| 141 | <H2><BR/><B>Q5 : Why doesn't libsndfile do interleaving/de-interleaving?</B></H2> |
| 142 | <P> |
| 143 | This problem is bigger than it may seem at first. |
| 144 | </P> |
| 145 | <P> |
| 146 | For a stereo file, it is a pretty safe bet that a simple interleaving/de-interleaving |
| 147 | could satisfy most users. |
| 148 | However, for files with more than 2 channels this is unlikely to be the case. |
| 149 | If the user has a 4 channel file and want to play that file on a stereo output |
| 150 | sound card they either want the first 2 channels or they want some mixed combination |
| 151 | of the 4 channels. |
| 152 | </P> |
| 153 | <P> |
| 154 | When you add more channels, the combinations grow exponentially and it becomes |
| 155 | increasingly difficult to cover even a sensible subset of the possible combinations. |
| 156 | On top of that, coding any one style of interleaver/de-interleaver is trivial, while |
| 157 | coding one that can cover all combinations is far from trivial. |
| 158 | This means that this feature will not be added any time soon. |
| 159 | </P> |
| 160 | |
| 161 | <!-- ========================================================================= --> |
| 162 | <A NAME="Q006"></A> |
| 163 | <H2><BR/><B>Q6 : What's the best format for storing temporary files?</B></H2> |
| 164 | |
| 165 | <P> |
| 166 | When you want to store temporary data there are a number of requirements; |
| 167 | </P> |
| 168 | <UL> |
| 169 | <LI> A simple, easy to parse header. |
| 170 | <LI> The format must provide the fastest possible read and write rates (ie |
| 171 | avoid conversions and encoding/decoding). |
| 172 | <LI> The file format must be reasonably common and playable by most players. |
| 173 | <LI> Able to store data in either endian-ness. |
| 174 | </UL> |
| 175 | <P> |
| 176 | The format which best meets these requirements is AU, which allows data to be |
| 177 | stored in any one of short, int, float and double (among others) formats. |
| 178 | </P> |
| 179 | <P> |
| 180 | For instance, if an application uses float data internally, its temporary files |
| 181 | should use a format of (SF_ENDIAN_CPU | SF_FORMAT_AU | SF_FORMAT_FLOAT) which |
| 182 | will store big endian float data in big endian CPUs and little endian float data |
| 183 | on little endian CPUs. |
| 184 | Reading and writing this format will not require any conversions or byte swapping |
| 185 | regardless of the host CPU. |
| 186 | </P> |
| 187 | |
| 188 | <!-- ========================================================================= --> |
| 189 | |
| 190 | <A NAME="Q007"></A> |
| 191 | <H2><BR/><B>Q7 : On Linux/Unix/MaxOS X, what's the best way of detecting the presence |
| 192 | of libsndfile using autoconf?</B></H2> |
| 193 | |
| 194 | <P> |
| 195 | libsndfile uses the pkg-config (man pkg-config) method of registering itself with the |
| 196 | host system. |
| 197 | The best way of detecting its presence is using something like this in configure.ac |
| 198 | (or configure.in): |
| 199 | </P> |
| 200 | <PRE> |
| 201 | PKG_CHECK_MODULES(SNDFILE, sndfile >= 1.0.2, ac_cv_sndfile=1, ac_cv_sndfile=0) |
| 202 | |
| 203 | AC_DEFINE_UNQUOTED([HAVE_SNDFILE],${ac_cv_sndfile}, |
| 204 | [Set to 1 if you have libsndfile.]) |
| 205 | |
| 206 | AC_SUBST(SNDFILE_CFLAGS) |
| 207 | AC_SUBST(SNDFILE_LIBS) |
| 208 | </PRE> |
| 209 | <P> |
| 210 | This will automatically set the <B>SNDFILE_CFLAGS</B> and <B>SNDFILE_LIBS</B> |
| 211 | variables which can be used in Makefile.am like this: |
| 212 | </P> |
| 213 | <PRE> |
| 214 | SNDFILE_CFLAGS = @SNDFILE_CFLAGS@ |
| 215 | SNDFILE_LIBS = @SNDFILE_LIBS@ |
| 216 | </PRE> |
| 217 | <P> |
| 218 | If you install libsndfile from source, you will probably need to set the |
| 219 | <B>PKG_CONFIG_PATH</B> environment variable as suggested at the end of the |
| 220 | libsndfile configure process. For instance on my system I get this: |
| 221 | </P> |
| 222 | <PRE> |
| 223 | -=-=-=-=-=-=-=-=-=-= Configuration Complete =-=-=-=-=-=-=-=-=-=- |
| 224 | |
| 225 | Configuration summary : |
| 226 | |
| 227 | Version : ..................... 1.0.5 |
| 228 | Experimental code : ........... no |
| 229 | |
| 230 | Tools : |
| 231 | |
| 232 | Compiler is GCC : ............. yes |
| 233 | GCC major version : ........... 3 |
| 234 | |
| 235 | Installation directories : |
| 236 | |
| 237 | Library directory : ........... /usr/local/lib |
| 238 | Program directory : ........... /usr/local/bin |
| 239 | Pkgconfig directory : ......... /usr/local/lib/pkgconfig |
| 240 | |
| 241 | Compiling some other packages against libsndfile may require |
| 242 | the addition of "/usr/local/lib/pkgconfig" to the |
| 243 | PKG_CONFIG_PATH environment variable. |
| 244 | </PRE> |
| 245 | |
| 246 | <!-- ========================================================================= --> |
| 247 | |
| 248 | <A NAME="Q008"></A> |
| 249 | <H2><BR/><B>Q8 : But I just want a simple Makefile! What do I do?</B></H2> |
| 250 | |
| 251 | <P> |
| 252 | The <B>pkg-config</B> program makes finding the correct compiler flag values and |
| 253 | library location far easier. |
| 254 | During the installation of libsndfile, a file named <B>sndfile.pc</B> is installed |
| 255 | in the directory <B>${libdir}/pkgconfig</B> (ie if libsndfile is installed in |
| 256 | <B>/usr/local/lib</B>, <B>sndfile.pc</B> will be installed in |
| 257 | <B>/usr/local/lib/pkgconfig/</B>). |
| 258 | </P> |
| 259 | <P> |
| 260 | In order for pkg-config to find sndfile.pc it may be necessary to point the |
| 261 | environment variable <B>PKG_CONFIG_PATH</B> in the right direction. |
| 262 | </P> |
| 263 | <PRE> |
| 264 | export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig |
| 265 | </PRE> |
| 266 | |
| 267 | <P> |
| 268 | Then, to compile a C file into an object file, the command would be: |
| 269 | </P> |
| 270 | <PRE> |
| 271 | gcc `pkg-config --cflags sndfile` -c somefile.c |
| 272 | </PRE> |
| 273 | <P> |
| 274 | and to link a number of objects into an executable that links against libsndfile, |
| 275 | the command would be: |
| 276 | </P> |
| 277 | <PRE> |
| 278 | gcc `pkg-config --libs sndfile` obj1.o obj2.o -o program |
| 279 | </PRE> |
| 280 | |
| 281 | <!-- ========================================================================= --> |
| 282 | |
| 283 | <A NAME="Q009"></A> |
| 284 | <H2><BR/><B>Q9 : How about adding the ability to write/read sound files to/from |
| 285 | memory buffers?</B></H2> |
| 286 | |
| 287 | <P> |
| 288 | This has been added for version 1.0.13. |
| 289 | </P> |
| 290 | |
| 291 | <!-- ========================================================================= --> |
| 292 | |
| 293 | <A NAME="Q010"></A> |
| 294 | <H2><BR/><B>Q10 : Reading a 16 bit PCM file as normalised floats and then |
| 295 | writing them back changes some sample values. Why?</B></H2> |
| 296 | |
| 297 | <P> |
| 298 | This is caused by the fact that the conversion from 16 bit short to float is |
| 299 | done by dividing by 32768 (0x8000 in hexadecimal) while the conversion from |
| 300 | float to 16 bit short is done by multiplying by 32767 (0x7FFF in hex). |
| 301 | So for instance, a value in a 16 bit PCM file of 20000 gets read as a floating |
| 302 | point number of 0.6103515625 (20000.0 / 0x8000). |
| 303 | Converting that back to a 16 bit short results in a value of 19999.3896484375 |
| 304 | (0.6103515625 * 0x7FFF) which then gets rounded down to 19999. |
| 305 | </P> |
| 306 | <P> |
| 307 | You will notice that for this particular case, the error is 1 in 20000 or |
| 308 | 0.005%. |
| 309 | Interestingly, for values of less than 16369, dividing by 0x8000 followed |
| 310 | by multiplying by 0x7FFF and then rounding the result, gives back the |
| 311 | original value. |
| 312 | It turns out that as long as the host operating system supplies the 1999 ISO |
| 313 | C Standard functions <B>lrintf</B> and <B>lrint</B> (or a replacement has |
| 314 | been supplied) then the maximum possible error is 1 in 16369 or about 0.006%. |
| 315 | </P> |
| 316 | <P> |
| 317 | Regardless of the size of the error, the reason why this is done is rather |
| 318 | subtle. |
| 319 | </P> |
| 320 | <P> |
| 321 | In a file containing 16 bit PCM samples, the values are restricted to the range |
| 322 | [-32768, 32767] while we want floating point values in the range [-1.0, 1.0]. |
| 323 | The only way to do this conversion is to do a floating point division by a value |
| 324 | of 0x8000. |
| 325 | Converting the other way, the only way to ensure that floating point values in |
| 326 | the range [-1.0, 1.0] are within the valid range allowed by a 16 bit short is |
| 327 | to multiply by 0x7FFF. |
| 328 | </P> |
| 329 | <P> |
| 330 | Some people would say that this is a severe short-coming of libsndfile. |
| 331 | I would counter that anybody who is constantly converting back and forth |
| 332 | between 16 bit shorts and normalised floats is going to suffer other losses |
| 333 | in audio quality that they should also be concerned about. |
| 334 | </P> |
| 335 | <P> |
| 336 | Since this problem only occurs when converting between integer data on disk and |
| 337 | normalized floats in the application, it can be avoided by using something |
| 338 | other than normalized floats in the application. |
| 339 | Alternatives to normalized floats are the <b>short</b> and <b>int</b> data |
| 340 | types (ie using sf_read_short or sf_read_int) or using un-normalized floats |
| 341 | (see |
| 342 | <a href="http://www.mega-nerd.com/libsndfile/command.html#SFC_SET_NORM_FLOAT"> |
| 343 | SFC_SET_NORM_FLOAT</a>). |
| 344 | </P> |
| 345 | <P> |
| 346 | Another way to deal with this problem is to consider 16 bit short data as a |
| 347 | final destination format only, not as an intermediate storage format. |
| 348 | All intermediate data (ie which is going to be processed further) should be |
| 349 | stored in floating point format which is supported by all of the most common |
| 350 | file formats. |
| 351 | If floating point files are considered too large (2 times the size of a 16 bit |
| 352 | PCM file), it would also be possible to use 24 bit PCM as an intermediate |
| 353 | storage format (and which is also supported by most common file types). |
| 354 | </P> |
| 355 | |
| 356 | <!-- ========================================================================= --> |
| 357 | |
| 358 | <A NAME="Q011"></A> |
| 359 | <H2><BR/><B>Q11 : I'm having problems with u-law encoded WAV files generated by |
| 360 | libsndfile in Winamp. Why? |
| 361 | </B></H2> |
| 362 | |
| 363 | <P> |
| 364 | This is actually a Winamp problem. |
| 365 | The official Microsoft spec suggests that the 'fmt ' chunk should be 18 bytes. |
| 366 | Unfortunately at least one of Microsoft's own applications (Sound Recorder on |
| 367 | Win98 I believe) did not accept 18 bytes 'fmt ' chunks. |
| 368 | </P> |
| 369 | <P> |
| 370 | Michael Lee did some experimenting and found that: |
| 371 | </P> |
| 372 | <PRE> |
| 373 | I have checked that Windows Media Player 9, QuickTime Player 6.4, |
| 374 | RealOne Player 2.0 and GoldWave 5.06 can all play u-law files with |
| 375 | 16-byte or 18-byte 'fmt ' chunk. Only Winamp (2.91) and foobar2000 |
| 376 | are unable to play u-law files with 16-byte 'fmt ' chunk. |
| 377 | </PRE> |
| 378 | |
| 379 | <P> |
| 380 | Even this is a very small sampling of all the players out there. |
| 381 | For that reason it is probably not a good idea to change this now because there |
| 382 | is the risk of breaking something that currently works. |
| 383 | </P> |
| 384 | |
| 385 | <!-- ========================================================================= --> |
| 386 | |
| 387 | <A NAME="Q012"></A> |
| 388 | <H2><BR/><B>Q12 : I'm looking at sf_read*. What are items? What are frames? |
| 389 | </B></H2> |
| 390 | |
| 391 | <P> |
| 392 | An <tt>item</tt>tt> is a single sample of the data type you are reading; ie a |
| 393 | single <tt>short</tt> value for <tt>sf_read_short</tt> or a single <tt>float</tt> |
| 394 | for <tt>sf_read_float</tt>. |
| 395 | </P> |
| 396 | |
| 397 | For a sound file with only one channel, a frame is the same as a item (ie a |
| 398 | single sample) while for multi channel sound files, a single frame contains a |
| 399 | single item for each channel. |
| 400 | </P> |
| 401 | |
| 402 | <P> |
| 403 | Here are two simple, correct examples, both of which are assumed to be working |
| 404 | on a stereo file, first using items: |
| 405 | </P> |
| 406 | |
| 407 | <PRE> |
| 408 | #define CHANNELS 2 |
| 409 | short data [CHANNELS * 100] ; |
| 410 | sf_count items_read = sf_read_short (file, data, 200) ; |
| 411 | assert (items_read == 200) ; |
| 412 | </PRE> |
| 413 | |
| 414 | <P> |
| 415 | and now readng the exact same amount of data using frames: |
| 416 | </P> |
| 417 | |
| 418 | <PRE> |
| 419 | #define CHANNELS 2 |
| 420 | short data [CHANNELS * 100] ; |
| 421 | sf_count frames_read = sf_readf_short (file, data, 100) ; |
| 422 | assert (frames_read == 100) ; |
| 423 | </PRE> |
| 424 | |
| 425 | <!-- ========================================================================= --> |
| 426 | |
| 427 | <A NAME="Q013"></A> |
| 428 | <H2><BR/><B>Q13 : Why can't libsndfile open this Sound Designer II (SD2) file? |
| 429 | </B></H2> |
| 430 | |
| 431 | <P> |
| 432 | This is somewhat complicated. |
| 433 | First some background. |
| 434 | </P> |
| 435 | |
| 436 | <P> |
| 437 | SD2 files are native to the Apple Macintosh platform and use features of |
| 438 | the Mac filesystem (file resource forks) to store the file's sample rate, |
| 439 | number of channels, sample width and more. |
| 440 | When you look at a file and its resource fork on Mac OS X it looks like |
| 441 | this: |
| 442 | </P> |
| 443 | |
| 444 | <PRE> |
| 445 | -rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2 |
| 446 | -rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 file.sd2/rsrc |
| 447 | </PRE> |
| 448 | |
| 449 | <P> |
| 450 | Notice how the file itself looks like a directory containing a single file |
| 451 | named <B>rsrc</B>. |
| 452 | When libsndfile is compiled for MacOS X, it should open (for write and read) |
| 453 | SD2 file with resource forks like this without any problems. |
| 454 | It will also handle files with the resource fork in a separate file as |
| 455 | described below. |
| 456 | </P> |
| 457 | |
| 458 | <P> |
| 459 | When SD2 files are moved to other platforms, the resource fork of the file |
| 460 | can sometimes be dropped altogether. |
| 461 | All that remains is the raw audio data and no information about the number |
| 462 | of channels, sample rate or bit width which makes it a little difficult for |
| 463 | libsndfile to open the file. |
| 464 | </P> |
| 465 | |
| 466 | <P> |
| 467 | However, it is possible to safely move an SD2 file to a Linux or Windows |
| 468 | machine. |
| 469 | For instance, when an SD2 file is copied from inside MacOS X to a windows |
| 470 | shared directory or a Samba share (ie Linux), MacOS X is clever enough to |
| 471 | store the resource fork of the file in a separate hidden file in the |
| 472 | same directory like this: |
| 473 | </P> |
| 474 | <PRE> |
| 475 | -rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 ._file.sd2 |
| 476 | -rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2 |
| 477 | </PRE> |
| 478 | |
| 479 | <P> |
| 480 | Regardless of what platform it is running on, when libsndfile is asked to |
| 481 | open a file named <B>"foo"</B> and it can't recognize the file type from |
| 482 | the data in the file, it will attempt to open the resource fork and if |
| 483 | that fails, it then tries to open a file named <B>"._foo"</B> to see if |
| 484 | the file has a valid resource fork. |
| 485 | This is the same regardless of whether the file is being opened for read |
| 486 | or write. |
| 487 | </P> |
| 488 | |
| 489 | <P> |
| 490 | In short, libsndfile should open SD2 files with a valid resource fork on |
| 491 | all of the platforms that libsndfile supports. |
| 492 | If a file has lost its resource fork, the only option is the open the file |
| 493 | using the SF_FORMAT_RAW option and guessing its sample rate, channel count |
| 494 | and bit width. |
| 495 | </P> |
| 496 | |
| 497 | <P> |
| 498 | Occasionally, when SD2 files are moved to other systems, the file is |
| 499 | <A HREF="http://www.macdisk.com/binhexen.php3">BinHexed</A> |
| 500 | which wraps the resource fork and the data fork together. |
| 501 | For these files, it would be possible to write a BinHex parser but |
| 502 | there is not a lot to gain considering how rare these BinHexed SD2 |
| 503 | files are. |
| 504 | </P> |
| 505 | |
| 506 | <!-- ========================================================================= --> |
| 507 | <A NAME="Q014"></A> |
| 508 | <H2><BR/><B>Q14 : I'd like to statically link libsndfile to my closed source |
| 509 | application. Can I buy a license so that this is possible? |
| 510 | </B></H2> |
| 511 | |
| 512 | <P> |
| 513 | Unfortunately no. |
| 514 | libsndfile contains code written by other people who have agreed that their |
| 515 | code be used under the GNU LGPL but no more. |
| 516 | Even if they were to agree, there would be significant difficulties in |
| 517 | dividing up the payments fairly. |
| 518 | </P> |
| 519 | |
| 520 | <P> |
| 521 | The <B>only</B> way you can legally use libsndfile as a statically linked |
| 522 | library is if your application is released under the GNU GPL or LGPL. |
| 523 | </P> |
| 524 | |
| 525 | <!-- ========================================================================= --> |
| 526 | <A NAME="Q015"></A> |
| 527 | <H2><BR/><B>Q15 : My program is crashing during a call to a function in libsndfile. |
| 528 | Is this a bug in libsndfile? |
| 529 | </B></H2> |
| 530 | |
| 531 | <P> |
| 532 | libsndfile is being used by large numbers of people all over the world |
| 533 | without any problems like this. That means that it is much more likely |
| 534 | that your code has a bug than libsndfile. However, it is still possible |
| 535 | that there is a bug in libsndfile. |
| 536 | </P> |
| 537 | <P> |
| 538 | To figure out whether it is your code or libsndfile you should do the |
| 539 | following: |
| 540 | </P> |
| 541 | <UL> |
| 542 | <LI>Make sure you are compiling your code with warnings switched on and |
| 543 | that you fix as many warnings as possible. |
| 544 | With the GNU compiler (gcc) I would recommend at least |
| 545 | <B>-W -Wall -Werror</B> which will force you to fix all warnings |
| 546 | before you can run the code. |
| 547 | <LI>Try using a memory debugger. |
| 548 | <A HREF="http://valgrind.kde.org/">Valgrind</A> on x86 Linux is excellent. |
| 549 | <A HREF="http://www.ibm.com/software/awdtools/purify/">Purify</A> also |
| 550 | has a good reputation. |
| 551 | <LI>If the code is clean after the above two steps and you still get |
| 552 | a crash in libsndfile, then send me a small snippet of code (no |
| 553 | more than 30-40 lines) which includes the call to sf_open() and |
| 554 | also shows how all variables passed to/returned from sf_open() |
| 555 | are defined. |
| 556 | </UL> |
| 557 | |
| 558 | <!-- ========================================================================= --> |
| 559 | <A NAME="Q016"></A> |
| 560 | <H2><BR/><B>Q16 : Will you accept a fix for compiling libsndfile with compiler X? |
| 561 | </B></H2> |
| 562 | |
| 563 | <P> |
| 564 | If compiler X is a C++ compiler then no. |
| 565 | C and C++ are different enough to make writing code that compiles as valid C |
| 566 | and valid C++ too difficult. |
| 567 | I would rather spend my time fixing bugs and adding features. |
| 568 | </P> |
| 569 | |
| 570 | <P> |
| 571 | If compiler X is a C compiler then I will do what I can as long as that does |
| 572 | not hamper the correctness, portability and maintainability of the existing |
| 573 | code. |
| 574 | It should be noted however that libsndfile uses features specified by the 1999 |
| 575 | ISO C Standard. |
| 576 | This can make compiling libsndfile with some older compilers difficult. |
| 577 | </P> |
| 578 | |
| 579 | <!-- ========================================================================= --> |
| 580 | <A NAME="Q017"></A> |
| 581 | <H2><BR/><B>Q17 : Can libsndfile read/write files from/to UNIX pipes? |
| 582 | </B></H2> |
| 583 | |
| 584 | <P> |
| 585 | Yes, libsndfile can read files from pipes. |
| 586 | Unfortunately, the write case is much more complicated. |
| 587 | </P> |
| 588 | |
| 589 | <P> |
| 590 | File formats like AIFF and WAV have information at the start of the file (the |
| 591 | file header) which states the length of the file, the number of sample frames |
| 592 | etc. |
| 593 | This information must be filled in correctly when the file header is written, |
| 594 | but this information is not reliably known until the file is closed. |
| 595 | This means that libsndfile cannot write AIFF, WAV and many other file types |
| 596 | to a pipe. |
| 597 | </P> |
| 598 | |
| 599 | <P> |
| 600 | However, there is at least one file format (AU) which is specifically designed |
| 601 | to be written to a pipe. |
| 602 | Like AIFF and WAV, AU has a header with a sample frames field, but it is |
| 603 | specifically allowable to set that frames field to 0x7FFFFFFF if the file |
| 604 | length is not known when the header is written. |
| 605 | The AU file format can also hold data in many of the standard formats (ie |
| 606 | SF_FORMAT_PCM_16, SF_FORMAT_PCM_24, SF_FORMAT_FLOAT etc) as well as allowing |
| 607 | data in both big and little endian format. |
| 608 | </P> |
| 609 | |
| 610 | <P> |
| 611 | See also <A HREF="#Q006">FAQ Q6</A>. |
| 612 | </P> |
| 613 | |
| 614 | <!-- ========================================================================= --> |
| 615 | <A NAME="Q018"></A> |
| 616 | <H2><BR/><B>Q18 : Is it possible to build a Universal Binary on Mac OS X? |
| 617 | </B></H2> |
| 618 | |
| 619 | <P> |
| 620 | Yes, but you must do two separate configure/build/test runs; one on PowerPC |
| 621 | and one on Intel. |
| 622 | It is then possible to merge the binaries into a single universal binary using |
| 623 | one of the programs in the Apple tool chain. |
| 624 | </P> |
| 625 | |
| 626 | <P> |
| 627 | It is <b>not</b> possible to build a working universal binary via a single |
| 628 | compile/build run on a single CPU. |
| 629 | </P> |
| 630 | |
| 631 | <P> |
| 632 | The problem is that the libsndfile build process detects features of the CPU its |
| 633 | being built for during the configure process and when building a universal binary, |
| 634 | configure is only run once and that data is then used for both CPUs. |
| 635 | That configure data will be wrong for one of those CPUs. |
| 636 | You will still be able to compile libsndfile, and the test suite will pass on |
| 637 | the machine you compiled it on. |
| 638 | However, if you take the universal binary test suite programs compiled on one |
| 639 | CPU and run them on the other, the test suite will fail. |
| 640 | </P> |
| 641 | |
| 642 | <P> |
| 643 | Part of the problem is the the CPU endian-ness is detected at configure time. |
| 644 | Yes, I know the Apple compiler defines one of the macros __LITTLE_ENDIAN__ |
| 645 | and __BIG_ENDIAN__, but those macros are not part of the 1999 ISO C Standard |
| 646 | and they are not portable. |
| 647 | </P> |
| 648 | |
| 649 | <P> |
| 650 | Endian issues are not the only reason why the cross compiled binary will fail. |
| 651 | The configure script also detects other CPU specific idiosyncrasies to provide |
| 652 | more optimized code. |
| 653 | </P> |
| 654 | |
| 655 | <P> |
| 656 | Finally, the real show stopper problem with universal binaries is the problem |
| 657 | with the test suite. |
| 658 | libsndfile contains a huge, comprehensive test suite. |
| 659 | When you compile a universal binary and run the test suite, you only test the |
| 660 | native compile. |
| 661 | The cross compiled binary (the one with the much higher chance of having |
| 662 | problems) cannot be tested. |
| 663 | </P> |
| 664 | |
| 665 | <P> |
| 666 | Now, if you have read this far you're probably thinking there must be a way |
| 667 | to fix this and there probably is. |
| 668 | The problem is that its a hell of a lot of work and would require significant |
| 669 | changes to the configure process, the internal code and the test suite. |
| 670 | In addition, these changes must not break compilation on any of the platforms |
| 671 | libsndfile is currently working on. |
| 672 | </p> |
| 673 | |
| 674 | |
| 675 | <!-- ========================================================================= --> |
| 676 | <A NAME="Q019"></A> |
| 677 | <H2><BR/><B>Q19 : I have project files for Visual Studio / XCode / Whatever. Why |
| 678 | don't you distribute them with libsndfile? |
| 679 | </B></H2> |
| 680 | |
| 681 | <P> |
| 682 | There's a very good reason for this. |
| 683 | I will only distribute things that I actually have an ability to test and |
| 684 | maintain. |
| 685 | Project files for a bunch of different compilers and Integrated Development |
| 686 | Environments are simply too difficult to maintain. |
| 687 | </P> |
| 688 | |
| 689 | <P> |
| 690 | The problem is that every time I add a new file to libsndfile or rename an |
| 691 | existing file I would have to modify all the project files and then test that |
| 692 | libsndfile still built with all the different compilers. |
| 693 | </P> |
| 694 | |
| 695 | <P> |
| 696 | Maintaining these project files is also rather difficult if I don't have access |
| 697 | to the required compiler/IDE. |
| 698 | If I just edit the project files without testing them I will almost certainly |
| 699 | get it wrong. |
| 700 | If I release a version of libsndfile with broken project files, I'll get a bunch |
| 701 | of emails from people complaining about it not building and have no way of |
| 702 | fixing or even testing it. |
| 703 | </P> |
| 704 | |
| 705 | <P> |
| 706 | I currently release sources that I personally test on Win32, Linux and |
| 707 | MacOS X (PowerPC) using the compiler I trust (GNU GCC). |
| 708 | Supporting one compiler on three (actually much more because GCC is available |
| 709 | almost everywhere) platforms is doable without too much pain. |
| 710 | I also release binaries for Win32 with instructions on how to use those |
| 711 | binaries with Visual Studio. |
| 712 | As a guy who is mainly interested in Linux, I'm not to keen to jump through |
| 713 | a bunch of hoops to support compilers and operating systems I don't use. |
| 714 | </P> |
| 715 | |
| 716 | <P> |
| 717 | So, I hear you want to volunteer to maintain the project files for Some Crappy |
| 718 | Compiler 2007? |
| 719 | Well sorry, that won't work either. |
| 720 | I have had numerous people over the years offer to maintaining the project |
| 721 | files for Microsoft's Visual Studio. |
| 722 | Every single time that happened, they maintained it for a release or two and |
| 723 | then disappeared off the face of the earth. |
| 724 | Hence, I'm not willing to enter into an arrangement like that again. |
| 725 | </P> |
| 726 | |
| 727 | <!-- ========================================================================= --> |
| 728 | <A NAME="Q020"></A> |
| 729 | <H2><BR/><B>Q20 : Why doesn't libsndfile support MP3? Lots of other Open Source |
| 730 | projects support it! |
| 731 | </B></H2> |
| 732 | |
| 733 | <P> |
| 734 | MP3 is not supported for one very good reason; doing so requires the payment |
| 735 | of licensing fees. |
| 736 | As can be seen from |
| 737 | <a href="http://www.mp3licensing.com/royalty/software.html"> |
| 738 | mp3licensing.com</a> |
| 739 | the required royalty payments are not cheap. |
| 740 | </P> |
| 741 | |
| 742 | <p> |
| 743 | Yes, I know other libraries ignore the licensing requirements, but their legal |
| 744 | status is extremely dubious. |
| 745 | At any time, the body selling the licenses could go after the authors of those |
| 746 | libraries. |
| 747 | Some of those authors may be students and hence wouldn't be worth pursuing. |
| 748 | </P> |
| 749 | |
| 750 | <p> |
| 751 | However, libsndfile is released under the name of a company, Mega Nerd Pty Ltd; |
| 752 | a company which has income from from libsamplerate licensing, libsndfile based |
| 753 | consulting income and other unrelated consulting income. |
| 754 | Adding MP3 support to libsndfile could place that income would be under legal |
| 755 | threat. |
| 756 | </p> |
| 757 | |
| 758 | <p> |
| 759 | Fortunately, Ogg Vorbis exists as an alternative to MP3. |
| 760 | Support for Ogg Vorbis was added to libsndfile (mostly due to the efforts of |
| 761 | John ffitch of the Csound project) in version 1.0.18. |
| 762 | </p> |
| 763 | |
| 764 | |
| 765 | <!-- ========================================================================= --> |
| 766 | <A NAME="Q021"></A> |
| 767 | <H2><BR/><B>Q21 : How do I use libsndfile in a closed source or commercial program |
| 768 | and comply with the license? |
| 769 | </B></H2> |
| 770 | |
| 771 | <p> |
| 772 | Here is a checklist of things you need to do to make sure your use of libsndfile |
| 773 | in a closed source or commercial project complies with the license libsndfile is |
| 774 | released under, the GNU Lesser General Public License (LGPL): |
| 775 | </p> |
| 776 | |
| 777 | <ul> |
| 778 | <li>Make sure you are linking to libsndfile as a shared library (Linux and Unix |
| 779 | systems), Dynamic Link Library (Microsoft Windows) or dynlib (Mac OS X). |
| 780 | If you are using some other operating system that doesn't allow dynamically |
| 781 | linked libraries, you will not be able to use libsndfile unless you release |
| 782 | the source code to your program. |
| 783 | <li>In the licensing documentation for your program, add a statement that your |
| 784 | software depends on libsndfile and that libsndfile is released under the GNU |
| 785 | Lesser General Public License, either |
| 786 | <a href="http://www.gnu.org/licenses/lgpl-2.1.txt">version 2.1</a> |
| 787 | or optionally |
| 788 | <a href="http://www.gnu.org/licenses/lgpl.txt">version 3</a>. |
| 789 | <li>Include the text for both versions of the license, possibly as separate |
| 790 | files named libsndfile_lgpl_v2_1.txt and libsndfile_lgpl_v3.txt. |
| 791 | </ul> |
| 792 | |
| 793 | <!-- ========================================================================= --> |
| 794 | <A NAME="Q022"></A> |
| 795 | <H2><BR/><B>Q22 : What versions of Windows does libsndfile work on? |
| 796 | </B></H2> |
| 797 | |
| 798 | <p> |
| 799 | Currently the precompiled windows binaries are thoroughly tested on Windows XP. |
| 800 | As such, they should also work on Win2k and Windows Vista. |
| 801 | They may also work on earlier versions of Windows. |
| 802 | </p> |
| 803 | |
| 804 | <p> |
| 805 | Since version 0.1.18 I have also been releasing precompiled binaries for Win64, |
| 806 | the 64 bit version of Windows. |
| 807 | These binaries have received much less testing than the 32 bit versions, but |
| 808 | should work as expected. |
| 809 | I'd be very interested in receiving feedback on these binaries. |
| 810 | </p> |
| 811 | |
| 812 | <!-- ========================================================================= --> |
| 813 | <A NAME="Q023"></A> |
| 814 | <H2><BR/><B>Q23 : I'm cross compiling libsndfile for another platform. How can I |
| 815 | run the test suite? |
| 816 | </B></H2> |
| 817 | |
| 818 | <p> |
| 819 | </p> |
| 820 | |
| 821 | <p> |
| 822 | Since version 1.0.21 the top level Makefile has an extra make target, |
| 823 | 'test-tarball'. |
| 824 | Building this target creates a tarball called called: |
| 825 | </p> |
| 826 | |
| 827 | <center><tt> |
| 828 | libsndfile-testsuite-${host_triplet}-${version}.tar.gz |
| 829 | </tt></center> |
| 830 | |
| 831 | <p> |
| 832 | in the top level directory. |
| 833 | This tarball can then be copied to the target platform. |
| 834 | Once untarred and test script <tt>test_wrapper.sh</tt> can be run from |
| 835 | the top level of the extracted tarball. |
| 836 | </p> |
| 837 | |
| 838 | <!-- ========================================================================= --> |
| 839 | <HR> |
| 840 | <P> |
| 841 | The libsndfile home page is here : |
| 842 | <A HREF="http://www.mega-nerd.com/libsndfile/"> |
| 843 | http://www.mega-nerd.com/libsndfile/</A>. |
| 844 | <BR/> |
| 845 | Version : 1.0.25 |
| 846 | </P> |
| 847 | |
| 848 | </BODY> |
| 849 | </HTML> |