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<HTML>
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<HEAD>
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<TITLE>
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libsndfile : Frequently Asked Questions.
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</TITLE>
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<META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)">
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<META NAME="Description" CONTENT="The libsndfile FAQ.">
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<META NAME="Keywords" CONTENT="WAV AIFF AU libsndfile sound audio dsp Linux">
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<LINK REL="stylesheet" HREF="libsndfile.css" TYPE="text/css" MEDIA="all">
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<LINK REL="stylesheet" HREF="print.css" TYPE="text/css" MEDIA="print">
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</HEAD>
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<BODY>
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libsndfile : Frequently Asked Questions.
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Q1 : Do you plan to support XYZ codec in libsndfile?
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Q2 : In version 0 the SF_INFO struct had a pcmbitwidth field
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but version 1 does not. Why?
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Q3 : Compiling is really slow on MacOS X. Why?
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Q4 : When trying to compile libsndfile on Solaris I get a "bad
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substitution" error during linking. What can I do to fix this?
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Q5 : Why doesn't libsndfile do interleaving/de-interleaving?
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Q6 : What's the best format for storing temporary files?
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Q7 : On Linux/Unix/MacOS X, what's the best way of detecting the
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presence of libsndfile?
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Q8 : I have libsndfile installed and now I want to use it. I
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just want a simple Makefile! What do I do?
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Q9 : How about adding the ability to write/read sound files to/from
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memory buffers?
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Q10 : Reading a 16 bit PCM file as normalised floats and then
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writing them back changes some sample values. Why?
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Q11 : I'm having problems with u-law encoded WAV files generated by
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libsndfile in Winamp. Why?
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Q12 : I'm looking at sf_read*. What are items? What are frames?
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Q13 : Why can't libsndfile open this Sound Designer II (SD2)
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file?
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Q14 : I'd like to statically link libsndfile to my closed source
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application. Can I buy a license so that this is possible?
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Q15 : My program is crashing during a call to a function in libsndfile.
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Is this a bug in libsndfile?
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Q16 : Will you accept a fix for compiling libsndfile with compiler X?
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Q17 : Can libsndfile read/write files from/to UNIX pipes?
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Q18 : Is it possible to build a Universal Binary on Mac OS X?
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Q19 : I have project files for Visual Studio / XCode / Whatever. Why
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don't you distribute them with libsndfile?
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Q20 : Why doesn't libsndfile support MP3? Lots of other Open Source
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projects support it!
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Q21 : How do I use libsndfile in a closed source or commercial program
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and comply with the license?
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Q22 : What versions of windows does libsndfile work on?
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Q23 : I'm cross compiling libsndfile for another platform. How can I
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run the test suite?
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Q1 : Do you plan to support XYZ codec in libsndfile?
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If source code for XYZ codec is available under a suitable license (LGPL, BSD,
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MIT etc) then yes, I'd like to add it.
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If suitable documentation is available on how to decode and encode the format
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then maybe, depending on how much work is involved.
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If XYZ is some proprietary codec where no source code or documentation is
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available then no.
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So if you want support for XYZ codec, first find existing source code or
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documentation.
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If you can't find either then the answer is no.
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Q2 : In version 0 the SF_INFO struct had a pcmbitwidth field
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but version 1 does not. Why?
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This was dropped for a number of reasons:
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pcmbitwidth makes little sense on compressed or floating point formats
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with the new API you really don't need to know it
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As documented
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here
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there is now a well defined behaviour which ensures that no matter what the
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bit width of the source file, the scaling always does something sensible.
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This makes it safe to read 8, 16, 24 and 32 bit PCM files using sf_read_short()
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and always have the optimal behaviour.
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Q3 : Compiling is really slow on MacOS X. Why?
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When you configure and compile libsndfile, it uses the /bin/sh shell for a number
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of tasks (ie configure script and libtool).
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Older versions of OS X (10.2?) shipped a really crappy Bourne shell as /bin/sh
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which resulted in really slow compiles.
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Newer version of OS X ship GNU Bash as /bin/sh and this answer doesn't apply in that
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case.
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To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to
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/bin/sh.old and make a symlink from /bin/sh to the bash shell.
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Bash is designed to behave as a Bourne shell when is is called as /bin/sh.
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When I did this on my iBook running MacOS X, compile times dropped from 13 minutes
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to 3 minutes.
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Q4 : When trying to compile libsndfile on Solaris I get a "bad
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substitution" error on linking. Why?
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It seems that the Solaris Bourne shell disagrees with GNU libtool.
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To fix this I suggest that you install the GNU Bash shell, rename /bin/sh to
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/bin/sh.old and make a symlink from /bin/sh to the bash shell.
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Bash is designed to behave as a Bourne shell when is is called as /bin/sh.
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Q5 : Why doesn't libsndfile do interleaving/de-interleaving?
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This problem is bigger than it may seem at first.
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For a stereo file, it is a pretty safe bet that a simple interleaving/de-interleaving
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could satisfy most users.
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However, for files with more than 2 channels this is unlikely to be the case.
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If the user has a 4 channel file and want to play that file on a stereo output
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sound card they either want the first 2 channels or they want some mixed combination
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of the 4 channels.
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When you add more channels, the combinations grow exponentially and it becomes
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increasingly difficult to cover even a sensible subset of the possible combinations.
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On top of that, coding any one style of interleaver/de-interleaver is trivial, while
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coding one that can cover all combinations is far from trivial.
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This means that this feature will not be added any time soon.
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Q6 : What's the best format for storing temporary files?
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When you want to store temporary data there are a number of requirements;
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A simple, easy to parse header.
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The format must provide the fastest possible read and write rates (ie
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avoid conversions and encoding/decoding).
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The file format must be reasonably common and playable by most players.
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Able to store data in either endian-ness.
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The format which best meets these requirements is AU, which allows data to be
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stored in any one of short, int, float and double (among others) formats.
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For instance, if an application uses float data internally, its temporary files
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should use a format of (SF_ENDIAN_CPU | SF_FORMAT_AU | SF_FORMAT_FLOAT) which
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will store big endian float data in big endian CPUs and little endian float data
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on little endian CPUs.
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Reading and writing this format will not require any conversions or byte swapping
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regardless of the host CPU.
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Q7 : On Linux/Unix/MaxOS X, what's the best way of detecting the presence
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of libsndfile using autoconf?
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libsndfile uses the pkg-config (man pkg-config) method of registering itself with the
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host system.
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The best way of detecting its presence is using something like this in configure.ac
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(or configure.in):
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PKG_CHECK_MODULES(SNDFILE, sndfile >= 1.0.2, ac_cv_sndfile=1, ac_cv_sndfile=0)
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AC_DEFINE_UNQUOTED([HAVE_SNDFILE],${ac_cv_sndfile},
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[Set to 1 if you have libsndfile.])
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AC_SUBST(SNDFILE_CFLAGS)
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AC_SUBST(SNDFILE_LIBS)
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This will automatically set the SNDFILE_CFLAGS and SNDFILE_LIBS
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variables which can be used in Makefile.am like this:
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SNDFILE_CFLAGS = @SNDFILE_CFLAGS@
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SNDFILE_LIBS = @SNDFILE_LIBS@
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If you install libsndfile from source, you will probably need to set the
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PKG_CONFIG_PATH environment variable as suggested at the end of the
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libsndfile configure process. For instance on my system I get this:
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-=-=-=-=-=-=-=-=-=-= Configuration Complete =-=-=-=-=-=-=-=-=-=-
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Configuration summary :
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Version : ..................... 1.0.5
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Experimental code : ........... no
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Tools :
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Compiler is GCC : ............. yes
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GCC major version : ........... 3
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Installation directories :
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Library directory : ........... /usr/local/lib
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Program directory : ........... /usr/local/bin
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Pkgconfig directory : ......... /usr/local/lib/pkgconfig
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Compiling some other packages against libsndfile may require
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the addition of "/usr/local/lib/pkgconfig" to the
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PKG_CONFIG_PATH environment variable.
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Q8 : I have libsndfile installed and now I want to use it. I just want
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a simple Makefile! What do I do?
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The pkg-config program makes finding the correct compiler flag values and
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library location far easier.
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During the installation of libsndfile, a file named sndfile.pc is installed
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in the directory ${libdir}/pkgconfig (ie if libsndfile is installed in
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/usr/local/lib, sndfile.pc will be installed in
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/usr/local/lib/pkgconfig/).
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In order for pkg-config to find sndfile.pc it may be necessary to point the
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environment variable PKG_CONFIG_PATH in the right direction.
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export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
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Then, to compile a C file into an object file, the command would be:
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gcc `pkg-config --cflags sndfile` -c somefile.c
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and to link a number of objects into an executable that links against libsndfile,
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the command would be:
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gcc `pkg-config --libs sndfile` obj1.o obj2.o -o program
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Q9 : How about adding the ability to write/read sound files to/from
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memory buffers?
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This has been added for version 1.0.13.
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Q10 : Reading a 16 bit PCM file as normalised floats and then
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writing them back changes some sample values. Why?
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This is caused by the fact that the conversion from 16 bit short to float is
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done by dividing by 32768 (0x8000 in hexadecimal) while the conversion from
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float to 16 bit short is done by multiplying by 32767 (0x7FFF in hex).
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So for instance, a value in a 16 bit PCM file of 20000 gets read as a floating
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point number of 0.6103515625 (20000.0 / 0x8000).
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Converting that back to a 16 bit short results in a value of 19999.3896484375
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(0.6103515625 * 0x7FFF) which then gets rounded down to 19999.
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You will notice that for this particular case, the error is 1 in 20000 or
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0.005%.
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Interestingly, for values of less than 16369, dividing by 0x8000 followed
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by multiplying by 0x7FFF and then rounding the result, gives back the
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original value.
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It turns out that as long as the host operating system supplies the 1999 ISO
|
|
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C Standard functions lrintf and lrint (or a replacement has
|
|
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been supplied) then the maximum possible error is 1 in 16369 or about 0.006%.
|
|
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Regardless of the size of the error, the reason why this is done is rather
|
|
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subtle.
|
|
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|
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In a file containing 16 bit PCM samples, the values are restricted to the range
|
|
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[-32768, 32767] while we want floating point values in the range [-1.0, 1.0].
|
|
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The only way to do this conversion is to do a floating point division by a value
|
|
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of 0x8000.
|
|
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Converting the other way, the only way to ensure that floating point values in
|
|
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the range [-1.0, 1.0] are within the valid range allowed by a 16 bit short is
|
|
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to multiply by 0x7FFF.
|
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Some people would say that this is a severe short-coming of libsndfile.
|
|
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I would counter that anybody who is constantly converting back and forth
|
|
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between 16 bit shorts and normalised floats is going to suffer other losses
|
|
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in audio quality that they should also be concerned about.
|
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|
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Since this problem only occurs when converting between integer data on disk and
|
|
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normalized floats in the application, it can be avoided by using something
|
|
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other than normalized floats in the application.
|
|
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Alternatives to normalized floats are the short and int data
|
|
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types (ie using sf_read_short or sf_read_int) or using un-normalized floats
|
|
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(see
|
|
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|
|
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SFC_SET_NORM_FLOAT).
|
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|
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Another way to deal with this problem is to consider 16 bit short data as a
|
|
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final destination format only, not as an intermediate storage format.
|
|
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All intermediate data (ie which is going to be processed further) should be
|
|
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stored in floating point format which is supported by all of the most common
|
|
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file formats.
|
|
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If floating point files are considered too large (2 times the size of a 16 bit
|
|
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4aff17 |
PCM file), it would also be possible to use 24 bit PCM as an intermediate
|
|
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storage format (and which is also supported by most common file types).
|
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|
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Q11 : I'm having problems with u-law encoded WAV files generated by
|
|
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4aff17 |
libsndfile in Winamp. Why?
|
|
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4aff17 |
|
|
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|
|
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4aff17 |
|
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This is actually a Winamp problem.
|
|
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The official Microsoft spec suggests that the 'fmt ' chunk should be 18 bytes.
|
|
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Unfortunately at least one of Microsoft's own applications (Sound Recorder on
|
|
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Win98 I believe) did not accept 18 bytes 'fmt ' chunks.
|
|
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|
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Michael Lee did some experimenting and found that:
|
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|
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|
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I have checked that Windows Media Player 9, QuickTime Player 6.4,
|
|
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RealOne Player 2.0 and GoldWave 5.06 can all play u-law files with
|
|
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16-byte or 18-byte 'fmt ' chunk. Only Winamp (2.91) and foobar2000
|
|
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are unable to play u-law files with 16-byte 'fmt ' chunk.
|
|
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4aff17 |
|
|
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|
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|
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Even this is a very small sampling of all the players out there.
|
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For that reason it is probably not a good idea to change this now because there
|
|
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is the risk of breaking something that currently works.
|
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|
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Q12 : I'm looking at sf_read*. What are items? What are frames?
|
|
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4aff17 |
|
|
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|
|
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|
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An <tt>item</tt> is a single sample of the data type you are reading; ie a
|
|
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4aff17 |
single <tt>short</tt> value for <tt>sf_read_short</tt> or a single <tt>float</tt>
|
|
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for <tt>sf_read_float</tt>.
|
|
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4aff17 |
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|
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|
|
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|
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For a sound file with only one channel, a frame is the same as a item (ie a
|
|
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4aff17 |
single sample) while for multi channel sound files, a single frame contains a
|
|
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4aff17 |
single item for each channel.
|
|
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4aff17 |
|
|
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|
|
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4aff17 |
|
|
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Here are two simple, correct examples, both of which are assumed to be working
|
|
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4aff17 |
on a stereo file, first using items:
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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#define CHANNELS 2
|
|
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short data [CHANNELS * 100] ;
|
|
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sf_count items_read = sf_read_short (file, data, 200) ;
|
|
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4aff17 |
assert (items_read == 200) ;
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
and now reading the exact same amount of data using frames:
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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#define CHANNELS 2
|
|
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short data [CHANNELS * 100] ;
|
|
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sf_count frames_read = sf_readf_short (file, data, 100) ;
|
|
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4aff17 |
assert (frames_read == 100) ;
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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Q13 : Why can't libsndfile open this Sound Designer II (SD2) file?
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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|
|
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4aff17 |
This is somewhat complicated.
|
|
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4aff17 |
First some background.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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|
|
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SD2 files are native to the Apple Macintosh platform and use features of
|
|
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4aff17 |
the Mac filesystem (file resource forks) to store the file's sample rate,
|
|
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4aff17 |
number of channels, sample width and more.
|
|
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4aff17 |
When you look at a file and its resource fork on Mac OS X it looks like
|
|
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4aff17 |
this:
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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|
|
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-rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2
|
|
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4aff17 |
-rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 file.sd2/rsrc
|
|
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4aff17 |
|
|
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|
|
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|
|
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Notice how the file itself looks like a directory containing a single file
|
|
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4aff17 |
named rsrc.
|
|
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4aff17 |
When libsndfile is compiled for MacOS X, it should open (for write and read)
|
|
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4aff17 |
SD2 file with resource forks like this without any problems.
|
|
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4aff17 |
It will also handle files with the resource fork in a separate file as
|
|
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4aff17 |
described below.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
When SD2 files are moved to other platforms, the resource fork of the file
|
|
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4aff17 |
can sometimes be dropped altogether.
|
|
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4aff17 |
All that remains is the raw audio data and no information about the number
|
|
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4aff17 |
of channels, sample rate or bit width which makes it a little difficult for
|
|
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4aff17 |
libsndfile to open the file.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
However, it is possible to safely move an SD2 file to a Linux or Windows
|
|
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4aff17 |
machine.
|
|
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4aff17 |
For instance, when an SD2 file is copied from inside MacOS X to a windows
|
|
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4aff17 |
shared directory or a Samba share (ie Linux), MacOS X is clever enough to
|
|
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4aff17 |
store the resource fork of the file in a separate hidden file in the
|
|
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4aff17 |
same directory like this:
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
-rw-r--r-- 1 erikd erikd 538 Oct 18 22:57 ._file.sd2
|
|
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4aff17 |
-rw-r--r-- 1 erikd erikd 46512 Oct 18 22:57 file.sd2
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Regardless of what platform it is running on, when libsndfile is asked to
|
|
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4aff17 |
open a file named "foo" and it can't recognize the file type from
|
|
Packit |
4aff17 |
the data in the file, it will attempt to open the resource fork and if
|
|
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4aff17 |
that fails, it then tries to open a file named "._foo" to see if
|
|
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4aff17 |
the file has a valid resource fork.
|
|
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4aff17 |
This is the same regardless of whether the file is being opened for read
|
|
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4aff17 |
or write.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
In short, libsndfile should open SD2 files with a valid resource fork on
|
|
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4aff17 |
all of the platforms that libsndfile supports.
|
|
Packit |
4aff17 |
If a file has lost its resource fork, the only option is the open the file
|
|
Packit |
4aff17 |
using the SF_FORMAT_RAW option and guessing its sample rate, channel count
|
|
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4aff17 |
and bit width.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Occasionally, when SD2 files are moved to other systems, the file is
|
|
Packit |
4aff17 |
BinHexed
|
|
Packit |
4aff17 |
which wraps the resource fork and the data fork together.
|
|
Packit |
4aff17 |
For these files, it would be possible to write a BinHex parser but
|
|
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4aff17 |
there is not a lot to gain considering how rare these BinHexed SD2
|
|
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4aff17 |
files are.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Q14 : I'd like to statically link libsndfile to my closed source
|
|
Packit |
4aff17 |
application. Can I buy a license so that this is possible?
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
Unfortunately no.
|
|
Packit |
4aff17 |
libsndfile contains code written by other people who have agreed that their
|
|
Packit |
4aff17 |
code be used under the GNU LGPL but no more.
|
|
Packit |
4aff17 |
Even if they were to agree, there would be significant difficulties in
|
|
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4aff17 |
dividing up the payments fairly.
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
The only way you can legally use libsndfile as a statically linked
|
|
Packit |
4aff17 |
library is if your application is released under the GNU GPL or LGPL.
|
|
Packit |
4aff17 |
|
|
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4aff17 |
|
|
Packit |
4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Q15 : My program is crashing during a call to a function in libsndfile.
|
|
Packit |
4aff17 |
Is this a bug in libsndfile?
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
libsndfile is being used by large numbers of people all over the world
|
|
Packit |
4aff17 |
without any problems like this. That means that it is much more likely
|
|
Packit |
4aff17 |
that your code has a bug than libsndfile. However, it is still possible
|
|
Packit |
4aff17 |
that there is a bug in libsndfile.
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
To figure out whether it is your code or libsndfile you should do the
|
|
Packit |
4aff17 |
following:
|
|
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4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
Make sure you are compiling your code with warnings switched on and
|
|
Packit |
4aff17 |
that you fix as many warnings as possible.
|
|
Packit |
4aff17 |
With the GNU compiler (gcc) I would recommend at least
|
|
Packit |
4aff17 |
-W -Wall -Werror which will force you to fix all warnings
|
|
Packit |
4aff17 |
before you can run the code.
|
|
Packit |
4aff17 |
Try using a memory debugger.
|
|
Packit |
4aff17 |
Valgrind on x86 Linux is excellent.
|
|
Packit |
4aff17 |
Purify also
|
|
Packit |
4aff17 |
has a good reputation.
|
|
Packit |
4aff17 |
If the code is clean after the above two steps and you still get
|
|
Packit |
4aff17 |
a crash in libsndfile, then send me a small snippet of code (no
|
|
Packit |
4aff17 |
more than 30-40 lines) which includes the call to sf_open() and
|
|
Packit |
4aff17 |
also shows how all variables passed to/returned from sf_open()
|
|
Packit |
4aff17 |
are defined.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Q16 : Will you accept a fix for compiling libsndfile with compiler X?
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
If compiler X is a C++ compiler then no.
|
|
Packit |
4aff17 |
C and C++ are different enough to make writing code that compiles as valid C
|
|
Packit |
4aff17 |
and valid C++ too difficult.
|
|
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4aff17 |
I would rather spend my time fixing bugs and adding features.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
If compiler X is a C compiler then I will do what I can as long as that does
|
|
Packit |
4aff17 |
not hamper the correctness, portability and maintainability of the existing
|
|
Packit |
4aff17 |
code.
|
|
Packit |
4aff17 |
It should be noted however that libsndfile uses features specified by the 1999
|
|
Packit |
4aff17 |
ISO C Standard.
|
|
Packit |
4aff17 |
This can make compiling libsndfile with some older compilers difficult.
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
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4aff17 |
|
|
Packit |
4aff17 |
Q17 : Can libsndfile read/write files from/to UNIX pipes?
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
Yes, libsndfile can read files from pipes.
|
|
Packit |
4aff17 |
Unfortunately, the write case is much more complicated.
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
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4aff17 |
File formats like AIFF and WAV have information at the start of the file (the
|
|
Packit |
4aff17 |
file header) which states the length of the file, the number of sample frames
|
|
Packit |
4aff17 |
etc.
|
|
Packit |
4aff17 |
This information must be filled in correctly when the file header is written,
|
|
Packit |
4aff17 |
but this information is not reliably known until the file is closed.
|
|
Packit |
4aff17 |
This means that libsndfile cannot write AIFF, WAV and many other file types
|
|
Packit |
4aff17 |
to a pipe.
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
However, there is at least one file format (AU) which is specifically designed
|
|
Packit |
4aff17 |
to be written to a pipe.
|
|
Packit |
4aff17 |
Like AIFF and WAV, AU has a header with a sample frames field, but it is
|
|
Packit |
4aff17 |
specifically allowable to set that frames field to 0x7FFFFFFF if the file
|
|
Packit |
4aff17 |
length is not known when the header is written.
|
|
Packit |
4aff17 |
The AU file format can also hold data in many of the standard formats (ie
|
|
Packit |
4aff17 |
SF_FORMAT_PCM_16, SF_FORMAT_PCM_24, SF_FORMAT_FLOAT etc) as well as allowing
|
|
Packit |
4aff17 |
data in both big and little endian format.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
See also FAQ Q6.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Q18 : Is it possible to build a Universal Binary on Mac OS X?
|
|
Packit |
4aff17 |
|
|
Packit |
4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
Yes, but you must do two separate configure/build/test runs; one on PowerPC
|
|
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4aff17 |
and one on Intel.
|
|
Packit |
4aff17 |
It is then possible to merge the binaries into a single universal binary using
|
|
Packit |
4aff17 |
one of the programs in the Apple tool chain.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
It is not possible to build a working universal binary via a single
|
|
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4aff17 |
compile/build run on a single CPU.
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
|
|
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4aff17 |
The problem is that the libsndfile build process detects features of the CPU its
|
|
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being built for during the configure process and when building a universal binary,
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configure is only run once and that data is then used for both CPUs.
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That configure data will be wrong for one of those CPUs.
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You will still be able to compile libsndfile, and the test suite will pass on
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the machine you compiled it on.
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However, if you take the universal binary test suite programs compiled on one
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CPU and run them on the other, the test suite will fail.
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Part of the problem is that the CPU endian-ness is detected at configure time.
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Yes, I know the Apple compiler defines one of the macros __LITTLE_ENDIAN__
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and __BIG_ENDIAN__, but those macros are not part of the 1999 ISO C Standard
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and they are not portable.
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Endian issues are not the only reason why the cross compiled binary will fail.
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The configure script also detects other CPU specific idiosyncrasies to provide
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more optimized code.
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Finally, the real show stopper problem with universal binaries is the problem
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with the test suite.
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libsndfile contains a huge, comprehensive test suite.
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When you compile a universal binary and run the test suite, you only test the
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native compile.
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The cross compiled binary (the one with the much higher chance of having
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problems) cannot be tested.
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Now, if you have read this far you're probably thinking there must be a way
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to fix this and there probably is.
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The problem is that its a hell of a lot of work and would require significant
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changes to the configure process, the internal code and the test suite.
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In addition, these changes must not break compilation on any of the platforms
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libsndfile is currently working on.
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Q19 : I have project files for Visual Studio / XCode / Whatever. Why
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don't you distribute them with libsndfile?
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There's a very good reason for this.
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I will only distribute things that I actually have an ability to test and
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maintain.
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Project files for a bunch of different compilers and Integrated Development
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Environments are simply too difficult to maintain.
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The problem is that every time I add a new file to libsndfile or rename an
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existing file I would have to modify all the project files and then test that
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libsndfile still built with all the different compilers.
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Maintaining these project files is also rather difficult if I don't have access
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to the required compiler/IDE.
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If I just edit the project files without testing them I will almost certainly
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get it wrong.
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If I release a version of libsndfile with broken project files, I'll get a bunch
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of emails from people complaining about it not building and have no way of
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fixing or even testing it.
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I currently release sources that I personally test on Win32, Linux and
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MacOS X (PowerPC) using the compiler I trust (GNU GCC).
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Supporting one compiler on three (actually much more because GCC is available
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almost everywhere) platforms is doable without too much pain.
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I also release binaries for Win32 with instructions on how to use those
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binaries with Visual Studio.
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As a guy who is mainly interested in Linux, I'm not to keen to jump through
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a bunch of hoops to support compilers and operating systems I don't use.
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So, I hear you want to volunteer to maintain the project files for Some Crappy
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Compiler 2007?
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Well sorry, that won't work either.
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I have had numerous people over the years offer to maintaining the project
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files for Microsoft's Visual Studio.
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Every single time that happened, they maintained it for a release or two and
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then disappeared off the face of the earth.
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Hence, I'm not willing to enter into an arrangement like that again.
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Q20 : Why doesn't libsndfile support MP3? Lots of other Open Source
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projects support it!
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MP3 is not supported for one very good reason; doing so requires the payment
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of licensing fees.
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As can be seen from
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mp3licensing.com
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the required royalty payments are not cheap.
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Yes, I know other libraries ignore the licensing requirements, but their legal
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status is extremely dubious.
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At any time, the body selling the licenses could go after the authors of those
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libraries.
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Some of those authors may be students and hence wouldn't be worth pursuing.
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However, libsndfile is released under the name of a company, Mega Nerd Pty Ltd;
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a company which has income from from libsamplerate licensing, libsndfile based
|
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consulting income and other unrelated consulting income.
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Adding MP3 support to libsndfile could place that income under legal threat.
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Fortunately, Ogg Vorbis exists as an alternative to MP3.
|
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Support for Ogg Vorbis was added to libsndfile (mostly due to the efforts of
|
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John ffitch of the Csound project) in version 1.0.18.
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|
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Q21 : How do I use libsndfile in a closed source or commercial program
|
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and comply with the license?
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|
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Here is a checklist of things you need to do to make sure your use of libsndfile
|
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in a closed source or commercial project complies with the license libsndfile is
|
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released under, the GNU Lesser General Public License (LGPL):
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|
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|
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Make sure you are linking to libsndfile as a shared library (Linux and Unix
|
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systems), Dynamic Link Library (Microsoft Windows) or dynlib (Mac OS X).
|
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If you are using some other operating system that doesn't allow dynamically
|
|
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linked libraries, you will not be able to use libsndfile unless you release
|
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the source code to your program.
|
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In the licensing documentation for your program, add a statement that your
|
|
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software depends on libsndfile and that libsndfile is released under the GNU
|
|
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Lesser General Public License, either
|
|
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version 2.1
|
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or optionally
|
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version 3.
|
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Include the text for both versions of the license, possibly as separate
|
|
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files named libsndfile_lgpl_v2_1.txt and libsndfile_lgpl_v3.txt.
|
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|
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|
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Q22 : What versions of Windows does libsndfile work on?
|
|
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|
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|
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|
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Currently the precompiled windows binaries are thoroughly tested on Windows XP.
|
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As such, they should also work on Win2k and Windows Vista.
|
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They may also work on earlier versions of Windows.
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|
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|
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|
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Since version 0.1.18 I have also been releasing precompiled binaries for Win64,
|
|
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the 64 bit version of Windows.
|
|
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These binaries have received much less testing than the 32 bit versions, but
|
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should work as expected.
|
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I'd be very interested in receiving feedback on these binaries.
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|
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|
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|
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|
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Q23 : I'm cross compiling libsndfile for another platform. How can I
|
|
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run the test suite?
|
|
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|
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|
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|
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|
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|
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|
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Since version 1.0.21 the top level Makefile has an extra make target,
|
|
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'test-tarball'.
|
|
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Building this target creates a tarball called called:
|
|
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|
|
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|
|
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<center><tt>
|
|
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libsndfile-testsuite-${host_triplet}-${version}.tar.gz
|
|
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</tt></center>
|
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|
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|
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in the top level directory.
|
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This tarball can then be copied to the target platform.
|
|
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Once untarred and test script <tt>test_wrapper.sh</tt> can be run from
|
|
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the top level of the extracted tarball.
|
|
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|
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|
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|
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|
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|
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The libsndfile home page is here :
|
|
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|
|
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http://www.mega-nerd.com/libsndfile/.
|
|
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|
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Version : 1.0.28
|
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</BODY>
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</HTML>
|