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diff --git a/src/libmad/README b/src/libmad/README new file mode 100644 index 000000000..2bf564c84 --- /dev/null +++ b/src/libmad/README @@ -0,0 +1,241 @@ + + libmad - MPEG audio decoder library + Copyright (C) 2000-2003 Underbit Technologies, Inc. + + $Id: README,v 1.1 2003/08/14 03:57:13 shank Exp $ + +=============================================================================== + +INTRODUCTION + + MAD (libmad) is a high-quality MPEG audio decoder. It currently supports + MPEG-1 and the MPEG-2 extension to Lower Sampling Frequencies, as well as + the so-called MPEG 2.5 format. All three audio layers (Layer I, Layer II, + and Layer III a.k.a. MP3) are fully implemented. + + MAD does not yet support MPEG-2 multichannel audio (although it should be + backward compatible with such streams) nor does it currently support AAC. + + MAD has the following special features: + + - 24-bit PCM output + - 100% fixed-point (integer) computation + - completely new implementation based on the ISO/IEC standards + - distributed under the terms of the GNU General Public License (GPL) + + Because MAD provides full 24-bit PCM output, applications using MAD are + able to produce high quality audio. Even when the output device supports + only 16-bit PCM, applications can use the extra resolution to increase the + audible dynamic range through the use of dithering or noise shaping. + + Because MAD uses integer computation rather than floating point, it is + well suited for architectures without a floating point unit. All + calculations are performed with a 32-bit fixed-point integer + representation. + + Because MAD is a new implementation of the ISO/IEC standards, it is + unencumbered by the errors of other implementations. MAD is NOT a + derivation of the ISO reference source or any other code. Considerable + effort has been expended to ensure a correct implementation, even in cases + where the standards are ambiguous or misleading. + + Because MAD is distributed under the terms of the GPL, its redistribution + is not generally restricted, so long as the terms of the GPL are followed. + This means MAD can be incorporated into other software as long as that + software is also distributed under the GPL. (Should this be undesirable, + alternate arrangements may be possible by contacting Underbit.) + +=============================================================================== + +ABOUT THE CODE + + The code is optimized and performs very well, although specific + improvements can still be made. The output from the decoder library + consists of 32-bit signed linear fixed-point values that can be easily + scaled for any size PCM output, up to 24 bits per sample. + + The API for libmad can be found in the `mad.h' header file. Note that this + file is automatically generated, and will not exist until after you have + built the library. + + There are two APIs available, one high-level, and the other low-level. + With the low-level API, each step of the decoding process must be handled + explicitly, offering the greatest amount of control. With the high-level + API, after callbacks are configured, a single routine will decode an + entire bitstream. + + The high-level API may either be used synchronously or asynchronously. If + used asynchronously, decoding will occur in a separate process. + Communication is possible with the decoding process by passing control + messages. + + The file `minimad.c' contains an example usage of the libmad API that + shows only the bare minimum required to implement a useful decoder. It + expects a regular file to be redirected to standard input, and it sends + decoded 16-bit signed little-endian PCM samples to standard output. If a + decoding error occurs, it is reported to standard error and decoding + continues. Note that the scale() routine in this code is only provided as + an example; it rounds MAD's high-resolution samples down to 16 bits, but + does not perform any dithering or noise shaping. It is therefore not + recommended to use this routine as-is in your own code if sound quality is + important. + +Integer Performance + + To get the best possible performance, it is recommended that an assembly + version of the fixed-point multiply and related routines be selected. + Several such assembly routines have been written for various CPUs. + + If an assembly version is not available, a fast approximation version will + be used. This will result in reduced accuracy of the decoder. + + Alternatively, if 64-bit integers are supported as a datatype by the + compiler, another version can be used that is much more accurate. + However, using an assembly version is generally much faster and just as + accurate. + + More information can be gathered from the `fixed.h' header file. + + MAD's CPU-intensive subband synthesis routine can be further optimized at + the expense of a slight loss in output accuracy due to a modified method + for fixed-point multiplication with a small windowing constant. While this + is helpful for performance and the output accuracy loss is generally + undetectable, it is disabled by default and must be explicitly enabled. + + Under some architectures, other special optimizations may also be + available. + +Audio Quality + + The output from MAD has been found to satisfy the ISO/IEC 11172-4 + computational accuracy requirements for compliance. In most + configurations, MAD is a Full Layer III ISO/IEC 11172-3 audio decoder as + defined by the standard. + + When the approximation version of the fixed-point multiply is used, MAD is + a limited accuracy ISO/IEC 11172-3 audio decoder as defined by the + standard. + + MAD can alternatively be configured to produce output with less or more + accuracy than the default, as a tradeoff with performance. + + MAD produces output samples with a precision greater than 24 bits. Because + most output formats use fewer bits, typically 16, it is recommended that a + dithering algorithm be used (rather than rounding or truncating) to obtain + the highest quality audio. However, dithering may unfavorably affect an + analytic examination of the output (such as compliance testing); you may + therefore wish to use rounding in this case instead. + +Portability Issues + + GCC is preferred to compile the code, but other compilers may also work. + The assembly code in `fixed.h' depends on the inline assembly features of + your compiler. If you're not using GCC or MSVC++, you can either write + your own assembly macros or use the default (low quality output) version. + + The union initialization of `huffman.c' may not be portable to all + platforms when GCC is not used. + + The code should not be sensitive to word sizes or byte ordering, however + it does assume A % B has the same sign as A. + +=============================================================================== + +BUILDING AND INSTALLING + +Windows Platforms + + MAD can be built under Windows using either MSVC++ or Cygwin. A MSVC++ + project file can be found under the `msvc++' subdirectory. + + To build libmad using Cygwin, you will first need to install the Cygwin + tools: + + http://www.cygwin.com/ + + You may then proceed with the following POSIX instructions within the + Cygwin shell. + + Note that by default Cygwin will build a library that depends on the + Cygwin DLL. You can use MinGW to build a library that does not depend on + the Cygwin DLL. To do so, give the option --host=mingw32 to `configure'. + +POSIX Platforms (including Cygwin) + + The code is distributed with a `configure' script that will generate for + you a `Makefile' and a `config.h' for your platform. See the file + `INSTALL' for generic instructions. + + The specific options you may want to give `configure' are: + + --enable-speed optimize for speed over accuracy + + --enable-accuracy optimize for accuracy over speed + + --disable-debugging do not compile with debugging support, and + use more optimizations + + --disable-shared do not build a shared library + + Note that you need not specify one of --enable-speed or --enable-accuracy; + in its default configuration, MAD is optimized for both. You should only + use one of these options if you wish to compromise speed or accuracy for + the other. + + By default the package will build a shared library if possible for your + platform. If you want only a static library, use --disable-shared. + + It is not normally necessary to use the following options, but you may + fine-tune the configuration with them if desired: + + --enable-fpm=ARCH use the ARCH-specific version of the + fixed-point math assembly routines + (current options are: intel, arm, mips, + sparc, ppc; also allowed are: 64bit, approx) + + --enable-sso use the subband synthesis optimization, + with reduced accuracy + + --disable-aso do not use certain architecture-specific + optimizations + + By default an appropriate fixed-point assembly routine will be selected + for the configured host type, if it can be determined. Thus if you are + cross-compiling for another architecture, you should be sure either to + give `configure' a host type argument (--host) or to use an explicit + --enable-fpm option. + + If an appropriate assembly routine cannot be determined, the default + approximation version will be used. In this case, use of an alternate + --enable-fpm is highly recommended. + +Experimenting and Developing + + Further options for `configure' that may be useful to developers and + experimenters are: + + --enable-debugging enable diagnostic debugging support and + debugging symbols + + --enable-profiling generate `gprof' profiling code + + --enable-experimental enable code using the EXPERIMENTAL + preprocessor define + +=============================================================================== + +COPYRIGHT + + Please read the `COPYRIGHT' file for copyright and warranty information. + Also, the file `COPYING' contains the full text of the GNU GPL. + + Send inquiries, comments, bug reports, suggestions, patches, etc. to: + + Underbit Technologies, Inc. <support@underbit.com> + + See also the MAD home page on the Web: + + http://www.underbit.com/products/mad/ + +=============================================================================== + |