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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

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 mpg123-1.32.1-dev+20230926022201 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.erMsa/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 mpg123=139K
config: --disable-shared
build static: PASS libmpg123.a=386K mpg123=456K
config: --disable-8bit
build just no 8 bit: PASS libmpg123.so=256K mpg123=139K
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=119K mpg123=114K
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: --disable-string
build minimal libmpg123: PASS libmpg123.so=119K mpg123=114K
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: --disable-string --with-cpu=generic
build minimal generic libmpg123: PASS libmpg123.so=99K mpg123=114K

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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