You could access this page securely.

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

2021-09-06 thomas: Releasing mpg123 version 1.29.0:

build: added --enable-runtime-tables
libmpg123:
- Float decoder runtime table computation is back as option, based on suggestion and initial patch by Ethan Halsall for a smaller download size of the wasm decoder built from libmpg23. This only trims the size of the binary on disk (network), for runtime overhead and a bit of uneasyness about concurrency during table computation, which happens implicitly on handle initialization, only guarded by an integer flag. This does _not_ revive mpg123_init().
- The ID3v2 UTF-16 BOM check is now a straight-on loop and not a recursive function.

The BOM check fix has been added to the 1.25-fixes and 1.26-fixes branches to ease importing into stable/LTS packages. Small stacks could collide with recursion depth, better avoid that.

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 mpg123-20210917022201 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=4.323452e-06 (PASS) maxdiff=7.688999e-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=1.967806e-08 (PASS) maxdiff=1.499429e-07 (PASS)
fl2.bit:	RMS=1.971421e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=1.999570e-08 (PASS) maxdiff=1.359731e-07 (PASS)
fl4.bit:	RMS=1.907914e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=3.946813e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.057529e-08 (PASS) maxdiff=1.611188e-07 (PASS)
fl7.bit:	RMS=1.771573e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl8.bit:	RMS=1.858160e-08 (PASS) maxdiff=8.568168e-08 (PASS)
--> 24 bit integer output
fl1.bit:	RMS=4.109562e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl2.bit:	RMS=4.172630e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl3.bit:	RMS=4.138422e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl4.bit:	RMS=4.113546e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl5.bit:	RMS=4.760588e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.948095e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl7.bit:	RMS=4.191326e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl8.bit:	RMS=4.093231e-08 (PASS) maxdiff=1.192093e-07 (PASS)
--> 32 bit floating point output
fl1.bit:	RMS=1.967816e-08 (PASS) maxdiff=1.499429e-07 (PASS)
fl2.bit:	RMS=1.971406e-08 (PASS) maxdiff=1.117587e-07 (PASS)
fl3.bit:	RMS=1.999566e-08 (PASS) maxdiff=1.359731e-07 (PASS)
fl4.bit:	RMS=1.907893e-08 (PASS) maxdiff=1.266599e-07 (PASS)
fl5.bit:	RMS=3.946791e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl6.bit:	RMS=3.057533e-08 (PASS) maxdiff=1.611188e-07 (PASS)
fl7.bit:	RMS=1.771578e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl8.bit:	RMS=1.858169e-08 (PASS) maxdiff=8.568168e-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=4.147492e-06 (PASS) maxdiff=7.688999e-06 (PASS)
--> 32 bit integer output
fl10.bit:	RMS=1.779875e-08 (PASS) maxdiff=8.195639e-08 (PASS)
fl11.bit:	RMS=1.790183e-08 (PASS) maxdiff=9.313226e-08 (PASS)
fl12.bit:	RMS=1.783333e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl13.bit:	RMS=1.760971e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=3.843849e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl15.bit:	RMS=2.423592e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl16.bit:	RMS=1.945052e-08 (PASS) maxdiff=1.345761e-07 (PASS)
--> 24 bit integer output
fl10.bit:	RMS=4.093468e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl11.bit:	RMS=4.106162e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl12.bit:	RMS=4.103626e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl13.bit:	RMS=4.120309e-08 (PASS) maxdiff=5.960464e-08 (PASS)
fl14.bit:	RMS=4.669633e-08 (PASS) maxdiff=1.192093e-07 (PASS)
fl15.bit:	RMS=4.092171e-08 (PASS) maxdiff=1.788139e-07 (PASS)
fl16.bit:	RMS=4.156544e-08 (PASS) maxdiff=1.788139e-07 (PASS)
--> 32 bit floating point output
fl10.bit:	RMS=1.779875e-08 (PASS) maxdiff=8.195639e-08 (PASS)
fl11.bit:	RMS=1.790183e-08 (PASS) maxdiff=9.313226e-08 (PASS)
fl12.bit:	RMS=1.783330e-08 (PASS) maxdiff=8.940697e-08 (PASS)
fl13.bit:	RMS=1.760970e-08 (PASS) maxdiff=4.470348e-08 (PASS)
fl14.bit:	RMS=3.843845e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl15.bit:	RMS=2.423593e-08 (PASS) maxdiff=1.490116e-07 (PASS)
fl16.bit:	RMS=1.945013e-08 (PASS) maxdiff=1.345761e-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=2.140540e-08 (PASS) maxdiff=1.769513e-07 (PASS)
--> 24 bit integer output
compl.bit:	RMS=4.198308e-08 (PASS) maxdiff=1.788139e-07 (PASS)
--> 32 bit floating point output
compl.bit:	RMS=2.140540e-08 (PASS) maxdiff=1.769513e-07 (PASS)

==== Layer 3 intensity stereo ====
   (no official reference, comparing to mpg123 generic 24 bit)
--> 16 bit signed integer output
drumshort08kHz.bit:	RMS=4.348726e-06 (PASS) maxdiff=7.748604e-06 (PASS)
drumshort24kHz.bit:	RMS=4.366056e-06 (PASS) maxdiff=7.808208e-06 (PASS)
drumshort48kHz.bit:	RMS=4.375039e-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=3.673318e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=3.876633e-08 (PASS) maxdiff=7.450581e-07 (PASS)
drumshort48kHz.bit:	RMS=3.427224e-08 (PASS) maxdiff=2.682209e-07 (PASS)
mono-is-ms.bit:	RMS=3.361756e-08 (PASS) maxdiff=7.450581e-08 (PASS)
--> 24 bit integer output
drumshort08kHz.bit:	RMS=2.269405e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=2.647431e-08 (PASS) maxdiff=7.748604e-07 (PASS)
drumshort48kHz.bit:	RMS=1.662534e-08 (PASS) maxdiff=2.384186e-07 (PASS)
mono-is-ms.bit:	RMS=6.148859e-09 (PASS) maxdiff=5.960464e-08 (PASS)
--> 32 bit floating point output
drumshort08kHz.bit:	RMS=3.673324e-08 (PASS) maxdiff=4.172325e-07 (PASS)
drumshort24kHz.bit:	RMS=3.876634e-08 (PASS) maxdiff=7.450581e-07 (PASS)
drumshort48kHz.bit:	RMS=3.427221e-08 (PASS) maxdiff=2.682209e-07 (PASS)
mono-is-ms.bit:	RMS=3.361467e-08 (PASS) maxdiff=7.450581e-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   -I/tmp/mpg123-svn.Gh1h4/prefix/include  -c -o helpers.o helpers.c
CC custom_io.bin
CC chomp_strings.bin
CC more_bytes_on_second_decode.bin
CC 2859531_id3_tag_not_skipped_when_NO_ID3V2_is_defined.bin
CC less_bytes_after_seek2.bin
CC seek_accuracy.bin
CC out123_passthrough.bin
CC bug201_wrong_frame_buffer.bin
CC bug201_another_one.bin
CC basic_resync.bin
CC freeformat.bin
CC out123_errorlist.bin
CC premature_decoder_change.bin
CC less_bytes_after_seek.bin
CC frame_seek_weirdness.bin
CC string_alloc.bin
CC 2950218_extra_samples_seek_last_frame.bin
Running tests.
Starting tests, look into test.log for messages.
PASS|SKIP is good, FAIL is bad.

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

PASS

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.