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mpg123 - Fast console MPEG Audio Player and decoder library

The mpg123 distribution contains a real time MPEG 1.0/2.0/2.5 audio player/decoder for layers 1,2 and 3 (most commonly MPEG 1.0 layer 3 aka MP3), as well as re-usable decoding and output libraries. Among others, it works on GNU/Linux, MacOSX, the BSDs, Solaris, AIX, HPUX, SGI Irix, OS/2 and Cygwin or plain MS Windows (not all more exotic platforms tested regularily, but patches welcome). You may jump to the non-exhaustive list of features.

It is free software licensed under LGPL 2.1 .

Note that nowadays, the mpg123 decoder core can work with floating point or integer math and with some tuning between accuracy and performance at build-time, using assembly optimizations for several platforms, depending on your build configuration. There is detection and selection of assembly optimisations on x86, x86-64, and ARM at program runtime. It's fast, it's high-quality. Just use it;-)

Top News

2024-11-02 thomas: Releasing mpg123 version 1.32.9:

Here comes just a small followup to the release fixing CVE-2024-10573. I forgot to increase the reported library patchlevel last time and a build improvement for MSVCRT also went in.

  • libmpg123:
    • enable 64 bit offset path for MSVCRT and avoid warnings about MS's game about POSIX API with and without underscores (bug 373).
    • Increase the library patchlevel, as was forgotten on previous release. Now you can check for distversion >= 1.32.8 or mpg123 libversion >= 48 patchlevel 3 to see if you're vulnerable to CVE-2024-10573.

Head over to the download section for getting your hands on the release.

2024-10-26 thomas: Releasing mpg123 version 1.32.8: Frankenstein's Monster

Update: The buffer overflow got assigned the CVE ID CVE-2024-10573.

This is an important security update! There is possible buffer overflow (writing of decoded PCM samples beyond allocated output buffer) for streams that change output properties together with certain usage of libmpg123. This needed seeking around in the stream (including scanning it before actual decoding) to trigger. So, your usual web radio stream as obvious attack vector is unlikely, as you won't seek around in it. If you do work with stream dumps, usage of MPG123_NO_FRANKENSTEIN or the --no-frankenstein option to the mpg123 application is a workaround to avoid the formerly dangerous situation in earlier mpg123 releases. This also means that mpg123 will not decode streams of concatenated files with either varying format or leading Info frames past the first track anymore.

With this release, the parser has been improved not to store certain stream properties before actual MPEG frame data matching that property has been stored. This avoids the inconsistency that triggered the overflow. Also note that if you always use a fixed decoding buffer for full stereo of the maximum of 1152 samples per frame, times two and your choice of encoding, your application is also not susceptible.

Exploitation of this is not trivial, but I cannot rule out the possibility of gaining code execution. Your exploit payload needs to pass through an MPEG decoder and PCM synth before possibly reaching the CPU. Some heap corruption can follow at the least. So update or mitigate. If you run 1.32.x, there is no excuse not to get the the latest bugfix release now. Basically any version of mpg123 is affected by this, at least those that explicitly support so-called Frankenstein streams.

  • libmpg123:
    • Add sections to assembly to support PAC/BTI code for aarch64 (-mbranch-protection variants), thanks to Bill Roberts (github PR 15).
    • Prevent premature application of header info into decoding structure, at worst having triggered out-of-bounds writes of decoded PCM data (bug 322, again).
  • out123: Show --quiet in --longhelp.

Head over to the download section for getting your hands on the release.

2024-08-07 thomas: Releasing mpg123 version 1.32.7:
  • ports/cmake: Work around bug in CMake that does not detect FPU on Apple ARM CPUs (github PR 14).
  • Fix some laziness (func() to func(void)) for standards conformance.

Head over to the download section for getting your hands on the release.

2024-04-04 thomas: Releasing mpg123 version 1.32.6:
  • build: Detect forced 64 bit offsets on a dual-mode system that used to default to 32 bits and drop ambiguous suffix-less symbols in that case. This avoids subtle ABI breakage (causing memory corruption) with existing binaries and instead has them fail during runtime linking. You trigger that when having -D_FILE_OFFSET_BITS=64 in your compiler flags during mpg123 build.

Head over to the download section for getting your hands on the release.

2024-02-17 thomas: Releasing mpg123 version 1.32.5:
  • build:
    • CMake port uses CFLAGS for pulse/jack/tinyalsa properly now (bug 366).
    • CMake port links libsyn123 with libm now (bug 370).
  • libmpg123:
    • Fix --enable-portable (no usage of LFS_WRAP_NONE, bug 368).
    • Fix dct36 wrapper usage for x86-64 and NEON. Stupid (bug 367) and also avoid returning void.
    • Make ARM builds work with nagging (missing feature macros for std=c99).

Head over to the download section for getting your hands on the release.

2024-01-10 thomas: Releasing mpg123 version 1.32.4:
  • build:
    • Reorganize shared headers, API headers into src/include.
    • Use relative include paths, avoiding internal directories in CPPFLAGS except for config.h.
    • Group C99 feature checks and make several standard headers mandatory.
    • Get rid of SIZE_P, OFF_P and friends.
    • Only enforce dummy module together with libout123, to be able to build individual modules using --disable-components logic.
  • out123:
    • added --libversion
  • libmpg123:
    • Avoid indirect branches into the assembly routines by using C wrappers also for dct36, relieving us of the need to care for bti / endbr instructions for control flow integrity.

Head over to the download section for getting your hands on the release.

2023-10-02 thomas: Releasing mpg123 version 1.32.3:
  • ports/cmake: Only enable modules with GetThreadErrorMode() on Windows.
  • compat: Define EOVERFLOW for ancient Windows toolchains.
  • libmpg123, libsyn123: always ifdef LFS_LARGEFILE_64 (not just if)
  • libsyn123: re-introduce _32 wrappers in addition to suffix-less ones (regression from 1.31, bug 363)

This finally is, hopefully, the release to replace 1.31.x. This was a rough ride due to largefile API/ABI stuff being just … horror. I really, really, hope that I won't have to rework that another time.

Head over to the download section for getting your hands on the release.

2023-09-27 thomas: Releasing mpg123 version 1.32.2:
  • libmpg123: Re-introduce _64 symbols on native 64 bit offset platforms. This was a regression since 1.31 series. Sorry, too much cleanup, not enough testing.
  • build:
    • Better O_LARGEFILE logic, avoiding redefintion.
  • ports/cmake:
    • Require C99 (bug 360, among other points, thanks to Ozkan Sezer).
    • Fix broken O_LARGEFILE logic (bug 360).
    • Typo fix and cleanup, also manual SSE switch for Android on old x86 (bug 359).

Head over to the download section for getting your hands on the release.

2023-09-24 thomas: Releasing mpg123 version 1.32.1:
  • Include man pages again in tarball and install. We cannot avoid the empty man directory when disabling programs with autoconf.
  • Fix signal handler prototype, avoiding some justified warnings.
  • ports/cmake:
    • Include CheckTypeSize, which seems to be needed sometimes (bug 357).
    • Avoid O_LARGEFILE redefinition, logic closer to autoconf.

Head over to the download section for getting your hands on the release.

2023-09-23 thomas: Releasing mpg123 version 1.32.0:
  • build:
    • Move version handling out of configure.ac to ease other build systems.
    • Include "fmt123.h" instead of <fmt123.h> in main API headers to make it more likely the correct one is included (at least gcc picks the one in the same directory as the including header first).
    • All headers are build-independent now.
    • Fix build for picky linkers by avoiding definition of wrap_getcpuflags() where it is not used (spurious linker error to non-exitent getcpuflags(), bug 353).
    • Handle deprecation of C99 detection macro in autoconf 2.70.
    • No use of AC_SYS_LARGEFILE anymore for explicit handling and differing choice for the libraries and frontend programs.
    • Added --enable-portable and --disable-largefile to configure, removing the other largefile-related options.
    • Added --disable-components --enable-libmpg123 to only build libmpg123 (and likewise --enable-libout123, --enable-libout123-modules, --enable-libsyn123) to autoconf build. CMake build has something similar with BUILD_PROGRAMS and BUILD_LIBOUT123, which leave only libmpg123 and libsyn123 if disabled). (bug 351)
    • Consistent formatting of ./configure --help with AS_HELP_STRING().
  • ports/Sony_PSP: removed
  • mpg123:
    • Added --libversion.
    • Added proper A-B looping with terminal control key 'o', renamed --pauseloop to --presetloop.
    • Really get rid of mpg123_position() usage. (It was all lies before!)
    • Fix terminal progress info when seeking in stopped mode (1.31 regression).
    • Patch up interaction of output buffer with generic remote control, adding non-interruptible drain after P 3, and dropping buffer on QUIT.
    • Uppercase some generic control replies for consinstency: SILENCE, PROGRESS, MUTE, UNMUTE
  • libmpg123, libout123, libsyn123:
    • Bumped API version for version query functions.
    • Replaced nearly all symbol renames with explicit INT123_ prefix declarations (intsym.h close to empty now).
  • libout123:
    • Add sleep builtin output module (silent, but proper timing).
  • libsyn123:
    • Introduced SYN123_PORTABLE_API for an API without off_t and ssize_t (see NEWS.libsyn123).
  • libmpg123:
    • Internal I/O using explicit largefile support via off64_t, lseek64, fallback to plain 32 bit off_t.
    • Added explicit 64 bit API with 64 suffix (mpg123_tell64(), not mpg123_tell_64()). This allows full avoidance of ambiguus off_t. The API is always using 64 bit integers, regardless of internal implementation. (bug 344)
    • Introduced MPG123_PORTABLE_API for an API subset without off_t and ssize_t.
    • Made mpg123_seek() and friends ignore offset sign for SEEK_END (always seeking towards beginning, assuming negative offset) to make lseek()-conforming usage possible. Seeking beyond the end never made sense, so no loss of valid functionality.
  • Overall use of INT123_strerror(), trying to use thread-safe strerror_l() if possible.

Head over to the download section for getting your hands on the release.

For older news see the news archive

ISO MPEG compliance

This is a rough log of an automated compliance test on the mpg123 webserver (Xeon E3, GNU/Linux), using the test bitstreams from the ISO MPEG reference set. At least the floating point output should really be close enough to the reference.

Regarding the method: This is comparing mpg123's output (with gapless code deactivated) from reference bitstreams to the reference output. A simple RMS error measure is employed, relative to full scale, just summing over mono or stereo data indiscriminently. This is my interpretation of the rules... maximum allowed RMS=8.80967e-06, maximum signal difference 6.10352e-05. 

compliance test for mpg123-1.32.9+20241121022201 on Linux x86_64
First decoder in this list will be tested first, then generic: 
Supported decoders: AVX x86-64 generic generic_dither

Testing default decoder...

==== Layer 1 ====
--> 16 bit signed integer output
fl1.bit:	RMS=4.364373e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl2.bit:	RMS=4.353138e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl3.bit:	RMS=4.348759e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl4.bit:	RMS=4.403421e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl5.bit:	RMS=4.323446e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl6.bit:	RMS=4.389602e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl7.bit:	RMS=3.826083e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl8.bit:	RMS=4.362205e-06 (PASS) maxdiff=7.629395e-06 (PASS)
--> 32 bit integer output
fl1.bit:	RMS=1.967634e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl2.bit:	RMS=1.971686e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=2.002386e-08 (PASS) maxdiff=1.341105e-07 (PASS)
fl4.bit:	RMS=1.902169e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=3.655859e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.069318e-08 (PASS) maxdiff=1.629815e-07 (PASS)
fl7.bit:	RMS=1.768833e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl8.bit:	RMS=1.857219e-08 (PASS) maxdiff=8.428469e-08 (PASS)
--> 24 bit integer output
fl1.bit:	RMS=4.096055e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl2.bit:	RMS=4.156199e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl3.bit:	RMS=4.126996e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl4.bit:	RMS=4.100406e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl5.bit:	RMS=4.574976e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.920292e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl7.bit:	RMS=4.186568e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl8.bit:	RMS=4.104751e-08 (PASS) maxdiff=1.192093e-07 (PASS)
--> 32 bit floating point output
fl1.bit:	RMS=1.967635e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl2.bit:	RMS=1.971679e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=2.002391e-08 (PASS) maxdiff=1.341105e-07 (PASS)
fl4.bit:	RMS=1.902160e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=3.655860e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.069316e-08 (PASS) maxdiff=1.629815e-07 (PASS)
fl7.bit:	RMS=1.768828e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl8.bit:	RMS=1.857223e-08 (PASS) maxdiff=8.428469e-08 (PASS)

==== Layer 2 ====
--> 16 bit signed integer output
fl10.bit:	RMS=3.512100e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl11.bit:	RMS=3.837267e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl12.bit:	RMS=3.901071e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl13.bit:	RMS=4.379583e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl14.bit:	RMS=4.112578e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl15.bit:	RMS=4.388568e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl16.bit:	RMS=4.147495e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
fl10.bit:	RMS=1.777418e-08 (PASS) maxdiff=8.475035e-08 (PASS)
fl11.bit:	RMS=1.789150e-08 (PASS) maxdiff=9.685755e-08 (PASS)
fl12.bit:	RMS=1.780872e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl13.bit:	RMS=1.760690e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=3.361258e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl15.bit:	RMS=2.414684e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl16.bit:	RMS=1.924891e-08 (PASS) maxdiff=1.192093e-07 (PASS)
--> 24 bit integer output
fl10.bit:	RMS=4.086103e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl11.bit:	RMS=4.098320e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl12.bit:	RMS=4.095125e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl13.bit:	RMS=4.108581e-08 (PASS) maxdiff=5.960464e-08 (PASS)
fl14.bit:	RMS=4.444728e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl15.bit:	RMS=4.098525e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl16.bit:	RMS=4.146825e-08 (PASS) maxdiff=1.192093e-07 (PASS)
--> 32 bit floating point output
fl10.bit:	RMS=1.777416e-08 (PASS) maxdiff=8.475035e-08 (PASS)
fl11.bit:	RMS=1.789151e-08 (PASS) maxdiff=9.685755e-08 (PASS)
fl12.bit:	RMS=1.780868e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl13.bit:	RMS=1.760693e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=3.361258e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl15.bit:	RMS=2.414676e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl16.bit:	RMS=1.924847e-08 (PASS) maxdiff=1.192093e-07 (PASS)

==== Layer 3 ====
--> 16 bit signed integer output
compl.bit:	RMS=4.300912e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
compl.bit:	RMS=2.104434e-08 (PASS) maxdiff=1.881272e-07 (PASS)
--> 24 bit integer output
compl.bit:	RMS=4.170551e-08 (PASS) maxdiff=2.384186e-07 (PASS)
--> 32 bit floating point output
compl.bit:	RMS=2.104434e-08 (PASS) maxdiff=1.881272e-07 (PASS)

==== Layer 3 intensity stereo ====
   (no official reference, comparing to mpg123 generic 24 bit)
--> 16 bit signed integer output
drumshort08kHz.bit:	RMS=4.348691e-06 (PASS) maxdiff=7.629395e-06 (PASS)
drumshort24kHz.bit:	RMS=4.365981e-06 (PASS) maxdiff=7.688999e-06 (PASS)
drumshort48kHz.bit:	RMS=4.375106e-06 (PASS) maxdiff=8.106232e-06 (PASS)
mono-is-ms.bit:	RMS=4.389831e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
drumshort08kHz.bit:	RMS=3.281180e-08 (PASS) maxdiff=1.043081e-07 (PASS)
drumshort24kHz.bit:	RMS=3.282391e-08 (PASS) maxdiff=1.192093e-07 (PASS)
drumshort48kHz.bit:	RMS=4.068793e-08 (PASS) maxdiff=6.854534e-07 (PASS)
mono-is-ms.bit:	RMS=3.511104e-08 (PASS) maxdiff=2.197921e-07 (PASS)
--> 24 bit integer output
drumshort08kHz.bit:	RMS=3.600636e-09 (PASS) maxdiff=5.960464e-08 (PASS)
drumshort24kHz.bit:	RMS=2.518008e-09 (PASS) maxdiff=1.192093e-07 (PASS)
drumshort48kHz.bit:	RMS=2.917921e-08 (PASS) maxdiff=7.152557e-07 (PASS)
mono-is-ms.bit:	RMS=1.635551e-08 (PASS) maxdiff=1.788139e-07 (PASS)
--> 32 bit floating point output
drumshort08kHz.bit:	RMS=3.281174e-08 (PASS) maxdiff=1.043081e-07 (PASS)
drumshort24kHz.bit:	RMS=3.282395e-08 (PASS) maxdiff=1.192093e-07 (PASS)
drumshort48kHz.bit:	RMS=4.068791e-08 (PASS) maxdiff=6.854534e-07 (PASS)
mono-is-ms.bit:	RMS=3.511108e-08 (PASS) maxdiff=2.197921e-07 (PASS)

==== Overall result ====
PASS (limited or full)

Now the generic decoder:

==== Layer 1 ====
--> 16 bit signed integer output
fl1.bit:	RMS=4.364373e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl2.bit:	RMS=4.353138e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl3.bit:	RMS=4.348759e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl4.bit:	RMS=4.403421e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl5.bit:	RMS=4.323446e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl6.bit:	RMS=4.389641e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl7.bit:	RMS=3.826083e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl8.bit:	RMS=4.362205e-06 (PASS) maxdiff=7.629395e-06 (PASS)
--> 32 bit integer output
fl1.bit:	RMS=1.977733e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl2.bit:	RMS=1.980311e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=2.006633e-08 (PASS) maxdiff=1.341105e-07 (PASS)
fl4.bit:	RMS=1.911986e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=4.047884e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl6.bit:	RMS=3.178246e-08 (PASS) maxdiff=1.639128e-07 (PASS)
fl7.bit:	RMS=1.775744e-08 (PASS) maxdiff=1.043081e-07 (PASS)
fl8.bit:	RMS=1.866297e-08 (PASS) maxdiff=8.195639e-08 (PASS)
--> 24 bit integer output
fl1.bit:	RMS=4.119282e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl2.bit:	RMS=4.184623e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl3.bit:	RMS=4.153068e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl4.bit:	RMS=4.118697e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl5.bit:	RMS=4.816338e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl6.bit:	RMS=4.047773e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl7.bit:	RMS=4.191854e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl8.bit:	RMS=4.106042e-08 (PASS) maxdiff=1.192093e-07 (PASS)
--> 32 bit floating point output
fl1.bit:	RMS=1.977741e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl2.bit:	RMS=1.980280e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=2.006633e-08 (PASS) maxdiff=1.341105e-07 (PASS)
fl4.bit:	RMS=1.911983e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=4.047868e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl6.bit:	RMS=3.178251e-08 (PASS) maxdiff=1.639128e-07 (PASS)
fl7.bit:	RMS=1.775792e-08 (PASS) maxdiff=1.043081e-07 (PASS)
fl8.bit:	RMS=1.866297e-08 (PASS) maxdiff=8.195639e-08 (PASS)

==== Layer 2 ====
--> 16 bit signed integer output
fl10.bit:	RMS=3.512100e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl11.bit:	RMS=3.837267e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl12.bit:	RMS=3.901071e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl13.bit:	RMS=4.379583e-06 (PASS) maxdiff=7.629395e-06 (PASS)
fl14.bit:	RMS=4.112596e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl15.bit:	RMS=4.388557e-06 (PASS) maxdiff=7.688999e-06 (PASS)
fl16.bit:	RMS=4.147495e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
fl10.bit:	RMS=1.788206e-08 (PASS) maxdiff=8.195639e-08 (PASS)
fl11.bit:	RMS=1.798147e-08 (PASS) maxdiff=1.005828e-07 (PASS)
fl12.bit:	RMS=1.791770e-08 (PASS) maxdiff=8.568168e-08 (PASS)
fl13.bit:	RMS=1.770191e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=4.111211e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl15.bit:	RMS=2.477557e-08 (PASS) maxdiff=1.639128e-07 (PASS)
fl16.bit:	RMS=1.970979e-08 (PASS) maxdiff=1.490116e-07 (PASS)
--> 24 bit integer output
fl10.bit:	RMS=4.102704e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl11.bit:	RMS=4.113184e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl12.bit:	RMS=4.107583e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl13.bit:	RMS=4.127499e-08 (PASS) maxdiff=5.960464e-08 (PASS)
fl14.bit:	RMS=4.977907e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl15.bit:	RMS=4.145519e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl16.bit:	RMS=4.171672e-08 (PASS) maxdiff=1.788139e-07 (PASS)
--> 32 bit floating point output
fl10.bit:	RMS=1.788201e-08 (PASS) maxdiff=8.195639e-08 (PASS)
fl11.bit:	RMS=1.798150e-08 (PASS) maxdiff=1.005828e-07 (PASS)
fl12.bit:	RMS=1.791763e-08 (PASS) maxdiff=8.568168e-08 (PASS)
fl13.bit:	RMS=1.770194e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=4.111203e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl15.bit:	RMS=2.477554e-08 (PASS) maxdiff=1.639128e-07 (PASS)
fl16.bit:	RMS=1.970946e-08 (PASS) maxdiff=1.490116e-07 (PASS)

==== Layer 3 ====
--> 16 bit signed integer output
compl.bit:	RMS=4.300914e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
compl.bit:	RMS=2.147540e-08 (PASS) maxdiff=1.750886e-07 (PASS)
--> 24 bit integer output
compl.bit:	RMS=4.202659e-08 (PASS) maxdiff=1.788139e-07 (PASS)
--> 32 bit floating point output
compl.bit:	RMS=2.147539e-08 (PASS) maxdiff=1.750886e-07 (PASS)

==== Layer 3 intensity stereo ====
   (no official reference, comparing to mpg123 generic 24 bit)
--> 16 bit signed integer output
drumshort08kHz.bit:	RMS=4.348733e-06 (PASS) maxdiff=7.748604e-06 (PASS)
drumshort24kHz.bit:	RMS=4.366053e-06 (PASS) maxdiff=7.808208e-06 (PASS)
drumshort48kHz.bit:	RMS=4.375036e-06 (PASS) maxdiff=7.748604e-06 (PASS)
mono-is-ms.bit:	RMS=4.389819e-06 (PASS) maxdiff=7.629395e-06 (PASS)
--> 32 bit integer output
drumshort08kHz.bit:	RMS=3.685351e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=3.893594e-08 (PASS) maxdiff=7.450581e-07 (PASS)
drumshort48kHz.bit:	RMS=3.389556e-08 (PASS) maxdiff=2.607703e-07 (PASS)
mono-is-ms.bit:	RMS=3.372314e-08 (PASS) maxdiff=8.940697e-08 (PASS)
--> 24 bit integer output
drumshort08kHz.bit:	RMS=2.297661e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=2.677607e-08 (PASS) maxdiff=7.748604e-07 (PASS)
drumshort48kHz.bit:	RMS=1.460054e-08 (PASS) maxdiff=2.384186e-07 (PASS)
mono-is-ms.bit:	RMS=9.138218e-09 (PASS) maxdiff=5.960464e-08 (PASS)
--> 32 bit floating point output
drumshort08kHz.bit:	RMS=3.685353e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=3.893599e-08 (PASS) maxdiff=7.450581e-07 (PASS)
drumshort48kHz.bit:	RMS=3.389551e-08 (PASS) maxdiff=2.607703e-07 (PASS)
mono-is-ms.bit:	RMS=3.372002e-08 (PASS) maxdiff=8.940697e-08 (PASS)

==== Overall result ====
PASS (limited or full)

Depending on what integer quality mode you choose at compile time (and the decoder in use), the 16bit output can vary between PASS and LIMITED for fully or limited accuracy compliance. But keep in mind: For the integer output, you have to give +-1 for rounding... that's what I append to any integer number read from some measurement device anyway, by default. That minimum possible deviation already brings the output close (or over) the border of full compliance... that really does not mean that the output sounds bad! It shall be noted that a measure to improve subjective quality, namely the dithering before rounding to integers, can also increase the theoretical decoding error.

In the end, RMS values in the order of 10 to the power of -5 should sound just fine. To get 16bit output to PASS, you usually need to enable proper rounding using the --enable-int-quality configure flag, which is on by default since some time now. On a specific (older) system, you might consider turning that off for possibly a slight performance gain.

For comparisong with other decoders (as well as older incarnations of the mpg123 engine), have a read of the Underbit compliance tests. Actually, my testing method follows that example, including their quoting of ISO MPEG rules.

Regression tests

This is output from the rudimentary regression test suite (which should eventually merge several approaches we had on testing in the past), working on the periodic snapshot: 

cc -Os  -I/tmp/mpg123-svn.A5BIE/prefix/include  -c -o helpers.o helpers.c
CC 2859531_id3_tag_not_skipped_when_NO_ID3V2_is_defined.bin
CC 2950218_extra_samples_seek_last_frame.bin
CC basic_resync.bin
CC bug201_another_one.bin
CC bug201_wrong_frame_buffer.bin
CC chomp_strings.bin
CC custom_io.bin
CC frame_seek_weirdness.bin
CC freeformat.bin
CC less_bytes_after_seek2.bin
CC less_bytes_after_seek.bin
CC more_bytes_on_second_decode.bin
CC out123_errorlist.bin
CC out123_passthrough.bin
CC premature_decoder_change.bin
CC seek_accuracy.bin
CC string_alloc.bin
Running tests.
Starting tests, look into test.log for messages.
PASS|SKIP is good, FAIL is bad.

2859531_id3_tag_not_skipped_when_NO_ID3V2_is_defined:     PASS
2950218_extra_samples_seek_last_frame:                    PASS
basic_resync:                                             PASS
bug201_another_one:                                       PASS
bug201_wrong_frame_buffer:                                PASS
chomp_strings:                                            PASS
custom_io:                                                PASS
frame_seek_weirdness:                                     PASS
freeformat:                                               PASS
less_bytes_after_seek2:                                   PASS
less_bytes_after_seek:                                    PASS
more_bytes_on_second_decode:                              PASS
out123_errorlist:                                         PASS
out123_passthrough:                                       PASS
premature_decoder_change:                                 PASS
seek_accuracy:                                            PASS
string_alloc:                                             PASS

PASS

Build tests

Testing some build setups and looking at libmpg123 size. 

Testing builds ...
config:
build default: PASS
   libmpg123.so=264K libsyn123.so=74K libout123.so=55K mpg123=139K out123=62K
config: --disable-shared
build static: PASS
   libmpg123.a=389K libsyn123.a=94K libout123.a=87K mpg123=456K out123=150K
config: --enable-portable
build portable: PASS
   libmpg123.so=256K libsyn123.so=74K libout123.so=55K out123=62K
config: --disable-8bit
build just no 8 bit: PASS
   libmpg123.so=256K libsyn123.so=74K libout123.so=55K mpg123=139K out123=62K
config: --disable-buffer --disable-feeder
config: --disable-messages --disable-moreinfo
config: --disable-feature_report --disable-network
config: --disable-icy --disable-id3v2 --disable-ntom
config: --disable-8bit --disable-16bit --disable-32bit
config: --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
build minimal mpg123: PASS
   libmpg123.so=124K libsyn123.so=74K libout123.so=34K mpg123=115K out123=54K
config: --disable-buffer --disable-feeder
config: --disable-messages --disable-moreinfo
config: --disable-feature_report --disable-network
config: --disable-icy --disable-id3v2 --disable-ntom
config: --disable-8bit --disable-16bit --disable-32bit
config: --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
config: --enable-portable --disable-string
build minimal libmpg123: PASS
   libmpg123.so=111K
config: --disable-buffer --disable-feeder
config: --disable-messages --disable-moreinfo
config: --disable-feature_report --disable-network
config: --disable-icy --disable-id3v2 --disable-ntom
config: --disable-8bit --disable-16bit --disable-32bit
config: --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
config: --enable-portable --disable-string
config: --with-cpu=generic
build minimal generic libmpg123: PASS
   libmpg123.so=99K
config: --with-audio=dummy
build cross arm-linux-gnueabihf default: PASS
   libmpg123.so=264K libsyn123.so=74K libout123.so=55K mpg123=139K out123=62K
config: --with-audio=dummy --disable-buffer
config: --disable-feeder --disable-messages
config: --disable-moreinfo --disable-feature_report
config: --disable-network --disable-icy --disable-id3v2
config: --disable-ntom --disable-8bit --disable-16bit
config: --disable-32bit --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
build cross arm-linux-gnueabihf minimal mpg123: PASS
   libmpg123.so=124K libsyn123.so=74K libout123.so=34K mpg123=115K out123=54K
config: --with-audio=dummy --disable-buffer
config: --disable-feeder --disable-messages
config: --disable-moreinfo --disable-feature_report
config: --disable-network --disable-icy --disable-id3v2
config: --disable-ntom --disable-8bit --disable-16bit
config: --disable-32bit --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
config: --enable-portable --disable-string
build cross arm-linux-gnueabihf minimal libmpg123: PASS
   libmpg123.so=111K
config: --with-audio=dummy
build cross aarch64-linux-gnu default: PASS
   libmpg123.so=264K libsyn123.so=74K libout123.so=55K mpg123=139K out123=62K
config: --with-audio=dummy --disable-buffer
config: --disable-feeder --disable-messages
config: --disable-moreinfo --disable-feature_report
config: --disable-network --disable-icy --disable-id3v2
config: --disable-ntom --disable-8bit --disable-16bit
config: --disable-32bit --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
build cross aarch64-linux-gnu minimal mpg123: PASS
   libmpg123.so=124K libsyn123.so=74K libout123.so=34K mpg123=115K out123=54K
config: --with-audio=dummy --disable-buffer
config: --disable-feeder --disable-messages
config: --disable-moreinfo --disable-feature_report
config: --disable-network --disable-icy --disable-id3v2
config: --disable-ntom --disable-8bit --disable-16bit
config: --disable-32bit --disable-layer1 --disable-layer2
config: --enable-runtime-tables --disable-downsample
config: --disable-equalizer --disable-ieeefloat
config: --enable-portable --disable-string
build cross aarch64-linux-gnu minimal libmpg123: PASS
   libmpg123.so=111K

Needed computing power

A test (GNU/Linux OS) with 0.60-beta2 showed 3 % to 4 % CPU usage on decoding high quality VBR MP3 with a pentiumII laptop with 366MHz, while a pentium 100MHz can easily handle two mpg123 instances in realtime (plus the mixing daemon that works on decoded data). Well, and more recently, A Core2Duo P8600 core can do 500 times realtime decoding (a track nearly five minutes long decoded in half a second).

Also, we have reports from such devices as nintendo DS or Sony PSP, or various embedded systems...

Michael said once upon a time

Plays Layer 3 in stereo on an AMD-486-120Mhz or (of course) a faster machine.

Just for info: mpg123 plays an average 128bps stream, with about 66% in full quality on an AMD 486-133MHz machine.

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