Control interface to generic frontends

The generic remote interface allows frontends to easily control
mpg123 by commands through stdin/stdout. To start the generic
remote interface, start mpg123 with parameter -R.

In case of a frontend that starts mpg123 with the -s option to read the audio from stdout, the --remote-err option is automatically activated to send responses to stderr so that stdout stays clean for audio.

(Still the case?)
As an example it's used by IRMP3, a tool that allows you to
control mpg123 with a standard infrared remote control. See
http://www.fasta.fh-dortmund.de/users/andy/irmp3/ for more
information.

You can also specify --fifo <path> to create a named pipe at <path> and listen on that for commands instead stdin.
That way, you can deliberately control mpg123 by echoing into the named pipe from any terminal / program.
The command respones are still sent to standard out or standard error (depending on -s or --remote-err switches).


COMMAND CODES
-------------

You can get this info via the control command "help".

HELP/H: command listing (LONG/SHORT forms), command case insensitve

LOAD/L <trackname>: load and start playing resource <trackname>

LOADPAUSED/LP <trackname>: load and start playing resource <trackname>

PAUSE/P: pause playback

STOP/S: stop playback (closes file)

JUMP/J <frame>|<+offset>|<-offset>|<[+|-]seconds>s: jump to mpeg frame <frame> or change position by offset, same in seconds if number followed by "s"

VOLUME/V <percent>: set volume in % (0..100...); float value

RVA off|(mix|radio)|(album|audiophile): set rva mode

EQ/E <channel> <band> <value>: set equalizer value for frequency band on channel

SEEK/K <sample>|<+offset>|<-offset>: jump to output sample position <samples> or change position by offset

SEQ <bass> <mid> <treble>: simple eq setting...

SILENCE: be silent during playback (meaning silence in text form)

TAG/T: Print all available (ID3) tag info, for ID3v2 that gives output of all collected text fields, using the ID3v2.3/4 4-character 
names.

meaning of the @S stream info:
S <mpeg-version> <layer> <sampling freq> <mode(stereo/mono/...)> <mode_ext> <framesize> <stereo> <copyright> <error_protected> <emphasis> <bitrate> <extension> <vbr(0/1=yes/no)>
The @I lines after loading a track give some ID3 info, the format:
     @I ID3:artist  album  year  comment genretext
    where artist,album and comment are exactly 30 characters each, year is 4 characters, genre text unspecified.
    You will encounter "@I ID3.genre:<number>" and "@I ID3.track:<number>".
    Then, there is an excerpt of ID3v2 info in the structure

RESPONSE CODES
--------------

Note: mpg123 returns errors on stderr, so your frontend should
      look not only at stdout but also at stderr for responses.

@R MPG123 (ThOr) v3
	Startup version message. Rverything after MPG123 is auxilliary information about behaviour and command support, ID3v2 tag support is new in v3.

@I ID3:<a><b><c>
	Status message after loading a song (ID3 song info)
	a = title (exactly 30 chars)
	b = artist (exactly 30 chars)
	c = album (exactly 30 chars)
	d = year (exactly 4 chars)
	e = comment (exactly 30 chars)
	f = genre (string)

@I ID3.genre:<number>
@I ID3.track:<number>
	Optional lines with additional ID3v1 info (if present): Genre ID and track number in set.

@I ID3v2.title:<text>
	After loading a track with ID3v2 info, such lines occur for every line of the "title" data field and likewise for other fields (author, album, etc).

@I <a>
			Status message after loading a song (no ID3 song info)
			a = filename without path and extension

@S <a> <b> ...
	Stream info at beginning of playback, meaning
	S <mpeg-version> <layer> <sampling freq> <mode(stereo/mono/...)> <mode_ext> <framesize> <stereo> <copyright> <error_protected> <emphasis> <bitrate> <extension> <vbr(0/1=yes/no)>

@S <a> <b> <c> <d> <e> <f> <g> <h> <i> <j> <k> <l>
	Status message after loading a song (stream info)
	a = mpeg type (string)
	b = layer (int)
	c = sampling frequency (int)
	d = mode (string)
	e = mode extension (int)
	f = framesize (int)
	g = stereo (int)
	h = copyright (int)
	i = error protection (int)
	j = emphasis (int)
	k = bitrate (int)
	l = extension (int)

@F <a> <b> <c> <d>
	Status message during playing (frame info)
	a = framecount (int)
	b = frames left this song (int)
	c = seconds (float)
	d = seconds left (float)

@P <a>
	Playing status
	a = 0: playing stopped
	a = 1: playing paused
	a = 2: playing unpaused

@E <a>
	An error occured
	Errors may be also reported by mpg123 through
	stderr (without @E)
	a = error message (string)

@J <n>
	Jumped to frame n.

@RVA <mode>
	Switched to specified RVA mode.

@V <volume>%
	Set volume to specified value (float, percent).

@<x> : <y> : <z>
	Set equalizer value z for band y of channel x.

@bass: <b> mid: <m> treble: <t>
	Set simple equalizer control for bass, mid, treble.

@T <response from TAG command>
	The output is multiple lines, begin marked by "@T {", end by "@T }".
	ID3v1 data is like in the @I info lines, just with "@T" in front.
	An ID3v2 data field is introduced via ([ ... ] means optional):
		@T ID3v2.<NAME>[ [lang(<LANG>)] desc(<description>)]:
	The lines of data follow with "=" prefixed:
		@T =<one line of content in UTF-8 encoding>


Info about the equalizer control:

Cold Feet Audio Patch for MPG123

10.07.2002

This is a dirty little hack to enable the equalizer in mpg123's
generic_control interface.  It works like this, there are two
different channels on the equalizer and 32 frequencys.

The hack just enables mpg123's built in equalizer to run real-time.
We haven't built in any capability to save the eq, you're frontend
will have to handle that part, and init the eq on the startup of
mpg123.

K, it works like this:

#./mpg123 -R -  <---- This command will start mpg123 in 'frontend' mode.

If you want to send it some eq values you'd send it:
eq X Y V[ENTER]

X = The channel.  It can be either 0 or 1.  I haven't put any error checking
    in, so it probably wouldn't be a good idea to go out of bounds. (integer)
Y = This is the frequency, it can be 0 to 31.  0 being closer to treble and
    31 being closer to bass. (integer)
V = The raw value of your equalizer setting.  I've found that the values work 
    best between 0.00 and 3.00.  When mpg123 starts up, all of them are set
    to 1.00.

OK, have fun!  If you have any questions or found some bugs, please contact
nutcase@dtmf.org

Thanks,
nut

Note by Thomas Orgis: The contact appreas to be dead.
