mpg123(1) mpg123(1) NAME mpg123 - play audio MPEG 1.0/2.0 file (layers 1, 2 and 3) SYNOPSIS mpg123 [ -tscvqy01m24 ] [ -b size ] [ -k num ] [ -n num ] [ -f factor ] [ -r rate ] [ -g gain ] [ -a dev ] [ -o s | -o h | -o l ] [ -d n ] [ -h n ] [ -p proxy ] [ -@ file ] file ... | URL ... | - DESCRIPTION mpg123 reads one or more files (or standard input if ``-'' is specified) or URLs and plays them on the audio device (default) or outputs them to stdout. file/URL is assumed to be an MPEG-1/2 audio bit stream. OPTIONS mpg123 options may be either the traditional POSIX one letter options, or the GNU style long options. POSIX style options start with a single ``-'', while GNU long options start with ``--''. -t, --test Test mode. The audio stream is decoded, but no output occurs. -s, --stdout The decoded audio samples are written to standard output, instead of playing them through the audio device. This option must be used if your audio hardware is not supported by mpg123. The output format is raw (headerless) linear PCM audio data, 16 bit, stereo, host byte order. -c, --check Check for filter range violations, and report them for each frame if any occur. -v, --verbose Increase the verbosity level. For example, dis- plays the frame numbers during decoding. -q, --quiet Quiet. Suppress diagnostic messages. -y, --resync Try to resync and continue decoding if an error occurs in the input file. Also try to recover from certain broken headers. Useful if you have a bro- ken MPEG file, on which mpg123 normally gives up saying `Illegal header'. Be careful: Broken loca- tions in MPEG files might cause sharp, loud pops or clicks, which might damage your speakers if played too loud. 21 Apr 1997 1 mpg123(1) mpg123(1) -0, --single0; -1, --single1 Decode only channel 0 (left) or channel 1 (right), respectively. These options are available for stereo MPEG streams only. -m, --singlemix Mix both channels. This option is available for stereo MPEG layer-3 streams only. It takes less CPU time than full stereo decoding. -2, --2to1; -4, --4to1 Performs a downsampling of ratio 2:1 (22 kHz) or 4:1 (11 kHz) on the output stream, respectively. Saves some CPU cycles, but at least the 4:1 ratio sounds ugly. -b size, --buffer size Use an audio output buffer of size Kbytes. This is useful to bypass short periods of heavy system activity, which would normally cause the audio out- put to be interrupted. You should specify a buffer size of at least 1024 (i.e. 1 Mb, which equals about 6 seconds of audio data) or more; less than about 300 does not make much sense. The default is 0, which turns buffering off. -k num, --skip num Skip first num frames. By default the decoding starts at the first frame. -n num, --frames num Decode only num frames. By default the complete stream is decoded. -f factor, --scale factor Change scale factor (default: 32768). -r rate, --rate rate Set sample rate (default: automatic). You don't want to change this. -g gain, --gain gain Set audio hardware output gain (default: don't change). -a dev, --device dev Specify the audio device to use. The default is system-dependent (usually /dev/audio or /dev/dsp). Use this option if you have multiple audio devices and the default is not what you want. -o s, --speaker Direct audio output to the speaker. 21 Apr 1997 2 mpg123(1) mpg123(1) -o h, --headphones Direct audio output to the headphone connector. -o l, --lineout Direct audio output to the line-out connector. -d n, --doublespeed n Only play every n'th frame. This will cause the MPEG stream to be played n times faster, which can be used for special effects. Can also be combined with the --halfspeed option to play 3 out of 4 frames etc. Don't expect great sound quality when using this option. -h n, --halfspeed n Play each frame n times. This will cause the MPEG stream to be played at 1/n'th speed (n times slower), which can be used for special effects. Can also be combined with the --doublespeed option to double every third frame or things like that. Don't expect great sound quality when using this option. -p URL | none, --proxy URL | none The specified proxy will be used for HTTP requests. It should be specified as full URL (``http://host.domain:port/''), but the ``http://'' prefix, the port number and the trailing slash are optional (the default port is 80). Specifying none means not to use any proxy, and to retrieve files directly from the respective servers. See also the ``HTTP SUPPORT'' section. -@ file, --list file Read filenames and/or URLs of MPEG audio streams from the specified file in addition to the ones specified on the command line (if any). Note that file can be either an ordinary file, a dash ``-'' to indicate that a list of filenames/URLs is to be read from the standard input, or an URL pointing to a an appropriate list file. Note: only one -@ option can be used (if more than one is specified, only the last one will be recognized). OPERANDS The following operands are supported: file(s) The path name(s) of one or more input files. They must be valid MPEG-1/2 audio layer-1, -2 or -3 bit streams. If a dash ``-'' is specified, MPEG data will be read from the standard input. Further- more, any name starting with ``http://'' is recog- nized as URL (see next section). 21 Apr 1997 3 mpg123(1) mpg123(1) HTTP SUPPORT In addition to reading MPEG audio streams from ordinary files and from the standard input, mpg123 supports retrieval of MPEG audio files via the HTTP protocol, which is used in the World Wide Web (WWW). Such files are spec- ified using a so-called URL (universal resource location), which starts with ``http://''. When a file with that pre- fix is encountered, mpg123 attempts to open an HTTP con- nection to the server in order to retrieve that file to decode and play it. It is often useful to retrieve files through a WWW cache or so-called proxy. To accomplish this, mpg123 examines the environment for variables named MP3_HTTP_PROXY, http_proxy and HTTP_PROXY, in this order. The value of the first one that is set will be used as proxy specifica- tion. To override this, you can use the -p command line option (see the ``OPTIONS'' section). Specifying -p none will enforce contacting the server directly without using any proxy, even if one of the above environment variables is set. Note that, in order to play MPEG audio files from a WWW server, it is necessary that the connection to that server is fast enough. For example, a 128 kbit/s MPEG file requires the network connection to be at least 128 kbit/s (16 kbyte/s) plus protocol overhead. If you suffer from short network outages, you should try the -b option (buffer) to bypass such outages. If your network connec- tion is generally not fast enough to retrieve MPEG audio files in realtime, you can first download the files to your local harddisk (e.g. using lynx(1)) and then play them from there. INTERRUPT You can abort mpg123 at any time by pressing Ctrl-C. If you are playing multiple files, this will stop the current file and begin playing the next one. If you want to abort playing immediately instead of skipping to the next file, press Ctrl-C twice in short succession (within about one second). Note that the result of pressing Ctrl-C might not be audi- ble immediately, due to audio data buffering in the audio device. This delay is system dependent, but it is usually not more than one or two seconds. SEE ALSO lynx(1), sox(1), intro(1) NOTES MPEG audio decoding requires a good deal of CPU perfor- mance, especially layer-3. To decode it in realtime, you should have at least a Pentium, Alpha, SuperSparc or 21 Apr 1997 4 mpg123(1) mpg123(1) equivalent processor. You can also use the -singlemix option to decode mono only, which reduces the CPU load somewhat for layer-3 streams. See also the -2 and -4 options. If everything else fails, use the -s option to decode to standard output, direct it into a file and then use an appropriate utility to play that file. You might have to use a tool such as sox(1) to convert the output to an audio format suitable for your audio player. Also note that mpg123 always generates 16 bit stereo data (if one of the -single* options is used, two identical stereo channels are generated). If your hardware requires some other format, for example 8 bit mono, you also have to use a converter such as sox(1). If your system is generally fast enough to decode in real- time, but there are sometimes periods of heavy system load (such as cronjobs, users logging in remotely, starting of ``big'' programs etc.) causing the audio output to be interrupted, then you should use the -b option to use a buffer of at least 1000 Kbytes. BUGS Known bugs and limitations: MPEG-2, Layer 1 and 2 not tested. May not work. (Layer 3 should work.) Free format streams are not supported. Layer-1 support is not heavily tested. No CRC error checking is performed. There is currently no support for audio hardware on DEC Digital Unix, Ultrix and IBM AIX, therefore the -s option has to be used on those platforms. AUTHORS Main author: Michael Hipp Uses code (or at least ideas) from: MPEG Software Simulation Group (Base package) Philipp Knirsch (DCT36/man- ual unroll) Tobias Bading (subband synthesis) Jeff Tsay (DCT36) Thomas Woerner (SGI Audio) Damien Clermonte (HP-UX audio fixes) Oliver Fromme Internet references: http://www.sfs.nphil.uni-tuebingen.de/~hipp/mpg123.html 21 Apr 1997 5 mpg123(1) mpg123(1) http://www.heim3.tu-clausthal.de/~olli/mpg123/ (includes information about the mpg123 mailing list) The latest version is also available from here: ftp.tu-clausthal.de:/pub/unix/audio/mpg123 http://ftp.tu-clausthal.de/pub/unix/audio/mpg123 21 Apr 1997 6