-Q1 : Do you plan to support XYZ codec in libsndfile?
-Q2 : In version 0 the SF_INFO struct had a pcmbitwidth field
- but version 1 does not. Why?
-Q3 : Compiling is really slow on MacOS X. Why?
-Q4 : When trying to compile libsndfile on Solaris I get a "bad
- substitution" error during linking. What can I do to fix this?
-Q5 : Why doesn't libsndfile do interleaving/de-interleaving?
-Q6 : What's the best format for storing temporary files?
-Q7 : On Linux/Unix/MacOS X, what's the best way of detecting the
- presence of libsndfile?
-Q8 : But I just want a simple Makefile! What do I do?
-Q9 : How about adding the ability to write/read sound files to/from
- memory buffers?
-Q10 : Reading a 16 bit PCM file as normalised floats and then
- writing them back changes some sample values. Why?
-Q11 : I'm having problems with u-law encoded WAV files generated by
- libsndfile in Winamp. Why?
-Q12 : I'm looking at sf_read*. What are items? What are frames?
-Q13 : Why can't libsndfile open this Sound Designer II (SD2)
- file?
-Q14 : I'd like to statically link libsndfile to my closed source
- application. Can I buy a license so that this is possible?
-Q15 : My program is crashing during a call to a function in libsndfile.
- Is this a bug in libsndfile?
-Q16 : Will you accept a fix for compiling libsndfile with compiler X?
-
-Q17 : Can libsndfile read/write files from/to UNIX pipes?
-
-Q18 : Is it possible to build a Universal Binary on Mac OS X?
-
-Q19 : I have project files for Visual Studio / XCode / Whatever. Why
- don't you distribute them with libsndfile?
-
-Q20 : Why doesn't libsndfile support MP3? Lots of other Open Source
- projects support it!
-
-Q21 : How do I use libsndfile in a closed source or commercial program
- and comply with the license?
-
-Q22 : What versions of windows does libsndfile work on?
-
-Q23 : I'm cross compiling libsndfile for another platform. How can I
- run the test suite?
-
-
-If source code for XYZ codec is available under a suitable license (LGPL, BSD, -MIT etc) then yes, I'd like to add it. -
--If suitable documentation is available on how to decode and encode the format -then maybe, depending on how much work is involved. -
--If XYZ is some proprietary codec where no source code or documentation is -available then no. -
--So if you want support for XYZ codec, first find existing source code or -documentation. -If you can't find either then the answer is no. -
- - -- This was dropped for a number of reasons: -
--As documented - here -there is now a well defined behaviour which ensures that no matter what the -bit width of the source file, the scaling always does something sensible. -This makes it safe to read 8, 16, 24 and 32 bit PCM files using sf_read_short() -and always have the optimal behaviour. -
- - - --When you configure and compile libsndfile, it uses the /bin/sh shell for a number -of tasks (ie configure script and libtool). -Older versions of OS X (10.2?) shipped a really crappy Bourne shell as /bin/sh -which resulted in really slow compiles. -Newer version of OS X ship GNU Bash as /bin/sh and this answer doesn't apply in that -case. -
--To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to -/bin/sh.old and make a symlink from /bin/sh to the bash shell. -Bash is designed to behave as a Bourne shell when is is called as /bin/sh. -
--When I did this on my iBook running MacOS X, compile times dropped from 13 minutes -to 3 minutes. -
- - - --It seems that the Solaris Bourne shell disagrees with GNU libtool. -
--To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to -/bin/sh.old and make a symlink from /bin/sh to the bash shell. -Bash is designed to behave as a Bourne shell when is is called as /bin/sh. -
- - - --This problem is bigger than it may seem at first. -
--For a stereo file, it is a pretty safe bet that a simple interleaving/de-interleaving -could satisfy most users. -However, for files with more than 2 channels this is unlikely to be the case. -If the user has a 4 channel file and want to play that file on a stereo output -sound card they either want the first 2 channels or they want some mixed combination -of the 4 channels. -
--When you add more channels, the combinations grow exponentially and it becomes -increasingly difficult to cover even a sensible subset of the possible combinations. -On top of that, coding any one style of interleaver/de-interleaver is trivial, while -coding one that can cover all combinations is far from trivial. -This means that this feature will not be added any time soon. -
- - - --When you want to store temporary data there are a number of requirements; -
--The format which best meets these requirements is AU, which allows data to be -stored in any one of short, int, float and double (among others) formats. -
--For instance, if an application uses float data internally, its temporary files -should use a format of (SF_ENDIAN_CPU | SF_FORMAT_AU | SF_FORMAT_FLOAT) which -will store big endian float data in big endian CPUs and little endian float data -on little endian CPUs. -Reading and writing this format will not require any conversions or byte swapping -regardless of the host CPU. -
- - - - --libsndfile uses the pkg-config (man pkg-config) method of registering itself with the -host system. -The best way of detecting its presence is using something like this in configure.ac -(or configure.in): -
-
- PKG_CHECK_MODULES(SNDFILE, sndfile >= 1.0.2, ac_cv_sndfile=1, ac_cv_sndfile=0)
-
- AC_DEFINE_UNQUOTED([HAVE_SNDFILE],${ac_cv_sndfile},
- [Set to 1 if you have libsndfile.])
-
- AC_SUBST(SNDFILE_CFLAGS)
- AC_SUBST(SNDFILE_LIBS)
-
--This will automatically set the SNDFILE_CFLAGS and SNDFILE_LIBS -variables which can be used in Makefile.am like this: -
-- SNDFILE_CFLAGS = @SNDFILE_CFLAGS@ - SNDFILE_LIBS = @SNDFILE_LIBS@ --
-If you install libsndfile from source, you will probably need to set the -PKG_CONFIG_PATH environment variable as suggested at the end of the -libsndfile configure process. For instance on my system I get this: -
-- -=-=-=-=-=-=-=-=-=-= Configuration Complete =-=-=-=-=-=-=-=-=-=- - - Configuration summary : - - Version : ..................... 1.0.5 - Experimental code : ........... no - - Tools : - - Compiler is GCC : ............. yes - GCC major version : ........... 3 - - Installation directories : - - Library directory : ........... /usr/local/lib - Program directory : ........... /usr/local/bin - Pkgconfig directory : ......... /usr/local/lib/pkgconfig - - Compiling some other packages against libsndfile may require - the addition of "/usr/local/lib/pkgconfig" to the - PKG_CONFIG_PATH environment variable. -- - - - -
-The pkg-config program makes finding the correct compiler flag values and -library location far easier. -During the installation of libsndfile, a file named sndfile.pc is installed -in the directory ${libdir}/pkgconfig (ie if libsndfile is installed in -/usr/local/lib, sndfile.pc will be installed in -/usr/local/lib/pkgconfig/). -
--In order for pkg-config to find sndfile.pc it may be necessary to point the -environment variable PKG_CONFIG_PATH in the right direction. -
-- export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig -- -
-Then, to compile a C file into an object file, the command would be: -
-- gcc `pkg-config --cflags sndfile` -c somefile.c --
-and to link a number of objects into an executable that links against libsndfile, -the command would be: -
-- gcc `pkg-config --libs sndfile` obj1.o obj2.o -o program -- - - - -
-This has been added for version 1.0.13. -
- - - - --This is caused by the fact that the conversion from 16 bit short to float is -done by dividing by 32768 (0x8000 in hexadecimal) while the conversion from -float to 16 bit short is done by multiplying by 32767 (0x7FFF in hex). -So for instance, a value in a 16 bit PCM file of 20000 gets read as a floating -point number of 0.6103515625 (20000.0 / 0x8000). -Converting that back to a 16 bit short results in a value of 19999.3896484375 -(0.6103515625 * 0x7FFF) which then gets rounded down to 19999. -
--You will notice that for this particular case, the error is 1 in 20000 or -0.005%. -Interestingly, for values of less than 16369, dividing by 0x8000 followed -by multiplying by 0x7FFF and then rounding the result, gives back the -original value. -It turns out that as long as the host operating system supplies the 1999 ISO -C Standard functions lrintf and lrint (or a replacement has -been supplied) then the maximum possible error is 1 in 16369 or about 0.006%. -
--Regardless of the size of the error, the reason why this is done is rather -subtle. -
--In a file containing 16 bit PCM samples, the values are restricted to the range -[-32768, 32767] while we want floating point values in the range [-1.0, 1.0]. -The only way to do this conversion is to do a floating point division by a value -of 0x8000. -Converting the other way, the only way to ensure that floating point values in -the range [-1.0, 1.0] are within the valid range allowed by a 16 bit short is -to multiply by 0x7FFF. -
--Some people would say that this is a severe short-coming of libsndfile. -I would counter that anybody who is constantly converting back and forth -between 16 bit shorts and normalised floats is going to suffer other losses -in audio quality that they should also be concerned about. -
--Since this problem only occurs when converting between integer data on disk and -normalized floats in the application, it can be avoided by using something -other than normalized floats in the application. -Alternatives to normalized floats are the short and int data -types (ie using sf_read_short or sf_read_int) or using un-normalized floats -(see - - SFC_SET_NORM_FLOAT). -
--Another way to deal with this problem is to consider 16 bit short data as a -final destination format only, not as an intermediate storage format. -All intermediate data (ie which is going to be processed further) should be -stored in floating point format which is supported by all of the most common -file formats. -If floating point files are considered too large (2 times the size of a 16 bit -PCM file), it would also be possible to use 24 bit PCM as an intermediate -storage format (and which is also supported by most common file types). -
- - - - --This is actually a Winamp problem. -The official Microsoft spec suggests that the 'fmt ' chunk should be 18 bytes. -Unfortunately at least one of Microsoft's own applications (Sound Recorder on -Win98 I believe) did not accept 18 bytes 'fmt ' chunks. -
--Michael Lee did some experimenting and found that: -
-- I have checked that Windows Media Player 9, QuickTime Player 6.4, - RealOne Player 2.0 and GoldWave 5.06 can all play u-law files with - 16-byte or 18-byte 'fmt ' chunk. Only Winamp (2.91) and foobar2000 - are unable to play u-law files with 16-byte 'fmt ' chunk. -- -
-Even this is a very small sampling of all the players out there. -For that reason it is probably not a good idea to change this now because there -is the risk of breaking something that currently works. -
- - - - --An itemtt> is a single sample of the data type you are reading; ie a -single short value for sf_read_short or a single float -for sf_read_float. -
- -For a sound file with only one channel, a frame is the same as a item (ie a -single sample) while for multi channel sound files, a single frame contains a -single item for each channel. - - --Here are two simple, correct examples, both of which are assumed to be working -on a stereo file, first using items: -
- -- #define CHANNELS 2 - short data [CHANNELS * 100] ; - sf_count items_read = sf_read_short (file, data, 200) ; - assert (items_read == 200) ; -- -
-and now readng the exact same amount of data using frames: -
- -- #define CHANNELS 2 - short data [CHANNELS * 100] ; - sf_count frames_read = sf_readf_short (file, data, 100) ; - assert (frames_read == 100) ; -- - - - -
-This is somewhat complicated. -First some background. -
- --SD2 files are native to the Apple Macintosh platform and use features of -the Mac filesystem (file resource forks) to store the file's sample rate, -number of channels, sample width and more. -When you look at a file and its resource fork on Mac OS X it looks like -this: -
- -- -rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2 - -rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 file.sd2/rsrc -- -
-Notice how the file itself looks like a directory containing a single file -named rsrc. -When libsndfile is compiled for MacOS X, it should open (for write and read) -SD2 file with resource forks like this without any problems. -It will also handle files with the resource fork in a separate file as -described below. -
- --When SD2 files are moved to other platforms, the resource fork of the file -can sometimes be dropped altogether. -All that remains is the raw audio data and no information about the number -of channels, sample rate or bit width which makes it a little difficult for -libsndfile to open the file. -
- --However, it is possible to safely move an SD2 file to a Linux or Windows -machine. -For instance, when an SD2 file is copied from inside MacOS X to a windows -shared directory or a Samba share (ie Linux), MacOS X is clever enough to -store the resource fork of the file in a separate hidden file in the -same directory like this: -
-- -rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 ._file.sd2 - -rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2 -- -
-Regardless of what platform it is running on, when libsndfile is asked to -open a file named "foo" and it can't recognize the file type from -the data in the file, it will attempt to open the resource fork and if -that fails, it then tries to open a file named "._foo" to see if -the file has a valid resource fork. -This is the same regardless of whether the file is being opened for read -or write. -
- --In short, libsndfile should open SD2 files with a valid resource fork on -all of the platforms that libsndfile supports. -If a file has lost its resource fork, the only option is the open the file -using the SF_FORMAT_RAW option and guessing its sample rate, channel count -and bit width. -
- --Occasionally, when SD2 files are moved to other systems, the file is - BinHexed -which wraps the resource fork and the data fork together. -For these files, it would be possible to write a BinHex parser but -there is not a lot to gain considering how rare these BinHexed SD2 -files are. -
- - - --Unfortunately no. -libsndfile contains code written by other people who have agreed that their -code be used under the GNU LGPL but no more. -Even if they were to agree, there would be significant difficulties in -dividing up the payments fairly. -
- --The only way you can legally use libsndfile as a statically linked -library is if your application is released under the GNU GPL or LGPL. -
- - - --libsndfile is being used by large numbers of people all over the world -without any problems like this. That means that it is much more likely -that your code has a bug than libsndfile. However, it is still possible -that there is a bug in libsndfile. -
--To figure out whether it is your code or libsndfile you should do the -following: -
--If compiler X is a C++ compiler then no. -C and C++ are different enough to make writing code that compiles as valid C -and valid C++ too difficult. -I would rather spend my time fixing bugs and adding features. -
- --If compiler X is a C compiler then I will do what I can as long as that does -not hamper the correctness, portability and maintainability of the existing -code. -It should be noted however that libsndfile uses features specified by the 1999 -ISO C Standard. -This can make compiling libsndfile with some older compilers difficult. -
- - - --Yes, libsndfile can read files from pipes. -Unfortunately, the write case is much more complicated. -
- --File formats like AIFF and WAV have information at the start of the file (the -file header) which states the length of the file, the number of sample frames -etc. -This information must be filled in correctly when the file header is written, -but this information is not reliably known until the file is closed. -This means that libsndfile cannot write AIFF, WAV and many other file types -to a pipe. -
- --However, there is at least one file format (AU) which is specifically designed -to be written to a pipe. -Like AIFF and WAV, AU has a header with a sample frames field, but it is -specifically allowable to set that frames field to 0x7FFFFFFF if the file -length is not known when the header is written. -The AU file format can also hold data in many of the standard formats (ie -SF_FORMAT_PCM_16, SF_FORMAT_PCM_24, SF_FORMAT_FLOAT etc) as well as allowing -data in both big and little endian format. -
- --See also FAQ Q6. -
- - - --Yes, but you must do two separate configure/build/test runs; one on PowerPC -and one on Intel. -It is then possible to merge the binaries into a single universal binary using -one of the programs in the Apple tool chain. -
- --It is not possible to build a working universal binary via a single -compile/build run on a single CPU. -
- --The problem is that the libsndfile build process detects features of the CPU its -being built for during the configure process and when building a universal binary, -configure is only run once and that data is then used for both CPUs. -That configure data will be wrong for one of those CPUs. -You will still be able to compile libsndfile, and the test suite will pass on -the machine you compiled it on. -However, if you take the universal binary test suite programs compiled on one -CPU and run them on the other, the test suite will fail. -
- --Part of the problem is the the CPU endian-ness is detected at configure time. -Yes, I know the Apple compiler defines one of the macros __LITTLE_ENDIAN__ -and __BIG_ENDIAN__, but those macros are not part of the 1999 ISO C Standard -and they are not portable. -
- --Endian issues are not the only reason why the cross compiled binary will fail. -The configure script also detects other CPU specific idiosyncrasies to provide -more optimized code. -
- --Finally, the real show stopper problem with universal binaries is the problem -with the test suite. -libsndfile contains a huge, comprehensive test suite. -When you compile a universal binary and run the test suite, you only test the -native compile. -The cross compiled binary (the one with the much higher chance of having -problems) cannot be tested. -
- --Now, if you have read this far you're probably thinking there must be a way -to fix this and there probably is. -The problem is that its a hell of a lot of work and would require significant -changes to the configure process, the internal code and the test suite. -In addition, these changes must not break compilation on any of the platforms -libsndfile is currently working on. -
- - - - --There's a very good reason for this. -I will only distribute things that I actually have an ability to test and -maintain. -Project files for a bunch of different compilers and Integrated Development -Environments are simply too difficult to maintain. -
- --The problem is that every time I add a new file to libsndfile or rename an -existing file I would have to modify all the project files and then test that -libsndfile still built with all the different compilers. -
- --Maintaining these project files is also rather difficult if I don't have access -to the required compiler/IDE. -If I just edit the project files without testing them I will almost certainly -get it wrong. -If I release a version of libsndfile with broken project files, I'll get a bunch -of emails from people complaining about it not building and have no way of -fixing or even testing it. -
- --I currently release sources that I personally test on Win32, Linux and -MacOS X (PowerPC) using the compiler I trust (GNU GCC). -Supporting one compiler on three (actually much more because GCC is available -almost everywhere) platforms is doable without too much pain. -I also release binaries for Win32 with instructions on how to use those -binaries with Visual Studio. -As a guy who is mainly interested in Linux, I'm not to keen to jump through -a bunch of hoops to support compilers and operating systems I don't use. -
- --So, I hear you want to volunteer to maintain the project files for Some Crappy -Compiler 2007? -Well sorry, that won't work either. -I have had numerous people over the years offer to maintaining the project -files for Microsoft's Visual Studio. -Every single time that happened, they maintained it for a release or two and -then disappeared off the face of the earth. -Hence, I'm not willing to enter into an arrangement like that again. -
- - - --MP3 is not supported for one very good reason; doing so requires the payment -of licensing fees. -As can be seen from - - mp3licensing.com -the required royalty payments are not cheap. -
- --Yes, I know other libraries ignore the licensing requirements, but their legal -status is extremely dubious. -At any time, the body selling the licenses could go after the authors of those -libraries. -Some of those authors may be students and hence wouldn't be worth pursuing. -
- --However, libsndfile is released under the name of a company, Mega Nerd Pty Ltd; -a company which has income from from libsamplerate licensing, libsndfile based -consulting income and other unrelated consulting income. -Adding MP3 support to libsndfile could place that income would be under legal -threat. -
- --Fortunately, Ogg Vorbis exists as an alternative to MP3. -Support for Ogg Vorbis was added to libsndfile (mostly due to the efforts of -John ffitch of the Csound project) in version 1.0.18. -
- - - - --Here is a checklist of things you need to do to make sure your use of libsndfile -in a closed source or commercial project complies with the license libsndfile is -released under, the GNU Lesser General Public License (LGPL): -
- --Currently the precompiled windows binaries are thoroughly tested on Windows XP. -As such, they should also work on Win2k and Windows Vista. -They may also work on earlier versions of Windows. -
- --Since version 0.1.18 I have also been releasing precompiled binaries for Win64, -the 64 bit version of Windows. -These binaries have received much less testing than the 32 bit versions, but -should work as expected. -I'd be very interested in receiving feedback on these binaries. -
- - - --
- --Since version 1.0.21 the top level Makefile has an extra make target, -'test-tarball'. -Building this target creates a tarball called called: -
- --in the top level directory. -This tarball can then be copied to the target platform. -Once untarred and test script test_wrapper.sh can be run from -the top level of the extracted tarball. -
- - -
- The libsndfile home page is here :
-
- http://www.mega-nerd.com/libsndfile/.
-
-Version : 1.0.25
-