Bigloo provides various facilities for programming multimedia
applications. It provides functions for parsing images and sounds and
functions for controlling music players. All the functions, variables,
and classes presented in the document are accessible via the
multimedia library. Here is an example of module that uses this
library:
| ;; Extract the thumbnail of a digital photography.
(module thumbnail
   (library multimedia)
   (main main))
 (define (main argv)
   (when (and (pair? (cdr argv)) (file-exists? (cadr argv)))
      (let ((ex (jpeg-exif (cadr argv))))
          (when (exif? ex)
             (display (exif-thumbnail ex))))))
 | 
The multimedia library provides functions for accessing the metadata
generated by digital camera.
| 
The function| jpeg-exif file-name | bigloo multimedia procedure |  jpeg-exifextracts the EXIF 
(http://en.wikipedia.org/wiki/Exif) metadata of a JPEG file as created
by digital camera. The argumentfile-nameis the name of the JPEG 
file. If the file contains an EXIF section it is returned as an instance
of theexifclass. Otherwise, this function returns#f. | 
| 
Set the comment of the EXIF metadata section of the file file-name
to| jpeg-exif-comment-set! file-name text | bigloo multimedia procedure |  text. | 
| 
| exif | bigloo multimedia class |  
The instance of the| (class exif
   (version (default #f))
   (jpeg-encoding (default #f))
   (jpeg-compress (default #f))
   (comment (default #f))
   (commentpos (default #f))
   (commentlen (default #f))
   (date (default #f))
   (make (default #f))
   (model (default #f))
   (orientation (default 'landscape))
   (width (default #f))
   (height (default #f))
   (ewidth (default #f))
   (eheight (default #f))
   (xresolution (default #f))
   (yresolution (default #f))
   (resolution-unit (default #f))
   (focal-length (default #f))
   (flash (default #f))
   (fnumber (default #f))
   (iso (default #f))
   (shutter-speed-value (default #f))
   (exposure-time (default #f))
   (exposure-bias-value (default #f))
   (aperture (default #f))
   (metering-mode (default #f))
   (cdd-width (default #f))
   (focal-plane-xres (default #f))
   (focal-plane-units (default #f))
   (thumbnail (default #f))
   (thumbnail-path (default #f))
   (thumbnail-offset (default #f))
   (thumbnail-length (default #f)))
 |  exifclass maps the EXIF metadata found in JPEG
files into Bigloo objects. Since all fields are optional they are untyped. | 
| 
Parses an exif date, i.e., a string of characters, and returns 
corresponding date. Raises an| exif-date->date | bigloo multimedia procedure |  &io-parse-errorif the string does
not represents an exif date whose syntax is given by the following regular
expression:
 
 
|   [0-9][0-9][0-9]:[0-9][0-9]:[0-9][0-9] :[0-9][0-9]:[0-9][0-9]:[0-9][0-9]
 |  | 
 
The multimedia library provides an extensive set of functions for dealing
with music. It provides functions for accessing the metadata of certain
music file formats, it provides functions for controlling the volume
of the hardware mixers and it provides functions for playing and controlling
music playback.
| 19.2.1 Metadata and Playlist
 | 
| 
| read-m3u input-port | bigloo multimedia procedure |  
The function| write-m3u list output-port | bigloo multimedia procedure |  read-m3ureads a playlist expressed in the M3U
format frominput-portand returns a list of songs. The functionwrite-m3uencode such a list encoded in the M3U format to an
output port. | 
| 
| file-musictag file-name | bigloo multimedia procedure |  
| mp3-musictag file-name | bigloo multimedia procedure |  
| ogg-musictag file-name | bigloo multimedia procedure |  
These functions extract the metadata of a music file named| flac-musictag file-name | bigloo multimedia procedure |  file-name.
 The function
 mp3-musictagreturns the ID3 tag section if it
exists. Otherwise, it returns#f. The functionogg-musictagandflac-musictagreturns the vorbis comment if it exists. | 
| 
| musictag | bigloo multimedia class |  
This class is used as the base class of music tag formats.| (abstract-class musictag
   (title::bstring read-only)
   (artist::bstring read-only)
   (orchestra::obj read-only (default #f))
   (interpret::obj read-only (default #f))
   (album::bstring read-only)
   (year::int read-only)
   (comment::bstring read-only)
   (genre::bstring read-only)
   (track::int (default -1)))
 |  | 
| 
| id3::musictag | bigloo multimedia class |  
This class is used to reify the ID3 metadata used in the MP3 format.| (class id3::musictag
   version::bstring
   (orchestra::obj read-only (default #f))
   (conductor::obj read-only (default #f))
   (recording read-only (default #f))
   (cd::obj (default #f)))
 |  | 
| 
This class is used to reify the Vorbis comments of OGG and Flac files.| vorbis::musictag | bigloo multimedia class |  | 
 
Bigloo proposes various functions and classes for controlling the
audio volume of sound cards.
| 
| mixer | bigloo multimedia class |  
The field| (class mixer
   (devices::pair-nil (default '())))
 |  devicesis a list of available channels. | 
| 
Closes a mixer. The argument| mixer-close mix | bigloo multimedia procedure |  mixmust be an instance of
themixerclass. | 
| 
| mixer-volume-get mix channel | bigloo multimedia procedure |  
The function| mixer-volume-set! mix channel leftv rightv | bigloo multimedia procedure |  mixer-volume-getreturns the left and right volume
levels (two values) of thechannelof the mixermix. Thechannelis denoted by its name and is represented as a string of
characters. The argumentmixis an instance of themixerclass.
 The function
 mixer-volume-set!changes the audio level of a mixer
channel. | 
| 
| soundcard::mixer | bigloo multimedia class |  
The instances of the class| (class soundcard::mixer
   (device::bstring read-only))
 |  soundcard, a subclass of themixerclass, are used to access physical soundcard as supported
by operating systems. The class fielddevicestands for the name
of the system device (e.g.,"/dev/mixer"for the Linux
OS). During the initialization of the instance, the device is opened
and initialized. | 
 
Bigloo supports various functions for playing music. These functions
rely on two data structure: 
music players and 
music status.
The first ones are used to control player back-ends. The second ones are
used to get information about the music being played. The following 
example shows how a simple music player using either MPlayer, MPG123, or
MPC can be programmed with Bigloo.
| (module musicplay
   (library multimedia)
   (main main))
 (define (main args)
   (let ((files '())
	 (backend 'mplayer)
	 (command #f))
      (args-parse (cdr args)
	 (("--mpg123" (help "Select the mpg123 back-end"))
	  (set! backend 'mpg123))
	 (("--mpc" (help "Select the mpc back-end"))
	  (set! backend 'mpc))
	 (("--mplayer" (help "Select the mplayer back-end"))
	  (set! backend 'mplayer))
	 (("--command" ?cmd (help "Set the command path"))
	  (set! command cmd))
	 (("--help" (help "This help"))
	  (print "usage: music [options] file ...")
	  (args-parse-usage #f)
	  (exit 0))
	 (else
	  (set! files (cons else files))))
      ;; create a music player
      (let ((player (case backend
		       ((mpg123)
			(if command
			    (instantiate::mpg123
			       (path command))
			    (instantiate::mpg123)))
		       ((mplayer)
			(if command
			    (instantiate::mplayer
			       (path command))
			    (instantiate::mplayer)))
		       ((mpc)
			(instantiate::mpc)))))
         ;; fill the music play list
	 (for-each (lambda (p) (music-playlist-add! player p)) (reverse files))
         ;; start playing
	 (music-play player)
         ;; run an event loop with call-backs associated to some events
	 (music-event-loop player
            :onstate (lambda (status)
                        (with-access::musicstatus status (state song volume)
                           (print "state   : " state)
                           (print "song    : " song)))
	    :onmeta (lambda (meta)
		       (print "meta    : " meta))
	    :onvolume (lambda (volume)
		       (print "volume  : " volume))))))
 | 
| 
| music | bigloo multimedia abstract class |  
This abstract class is the root class of all music players.| (abstract-class music
   (frequency::long (default 2000000))
 |  | 
| 
| musicproc::music | bigloo multimedia class |  
This class is used to reify player that are run in an external process.| (class musicproc::music
   (charset::symbol (default 'ISO-LATIN-1)))
 |  | 
| 
| mplayer::musicproc | bigloo multimedia class |  
A player based on the external software| (class mplayer::musicproc
   (path::bstring read-only (default "mplayer"))
   (args::pair-nil read-only (default '("-vo" "null" "-quiet" "-slave" "-idle")))
   (ao::obj read-only (default #unspecified))
   (ac::obj read-only (default #unspecified)))
 |  MPlayer. Creating such a player
spawns in background a MPlayer process.
 
 | 
| 
| mpg123::musicproc | bigloo multimedia class |  
A player based on the external software| (class mpg123::musicproc
   (path::bstring read-only (default "mpg123"))
   (args::pair-nil read-only (default '("--remote"))))
 |  mpg123.
 
 | 
| 
| mpc::music | bigloo multimedia class |  
A MPC client.| (class mpc::music
   (hello read-only (default #f))
   (host read-only (default "localhost"))
   (port read-only (default 6600))
   (timeout read-only (default 10008993))
   (prefix (default #f)))
 |  
 
 hello: an optional string written when the connection
is establish with the MPD server.prefix: an optional path prefix to be removed from music 
playlist. This is needed because MPD can only play music files registered
in is private database. The file names used by MPD are relative a 
root directory used to fill the database. Theprefixfield allows
programmer to write portable code that manages play list file names 
independently of the player selected.
 | 
| 
| musicstatus | bigloo multimedia class |  
The instances of the class| (class musicstatus
   (state::symbol (default 'stop))
   (volume::obj (default -1))
   (repeat::bool (default #f))
   (random::bool (default #f))
   (playlistid::int (default -1))
   (playlistlength::int (default 0))
   (xfade::int (default 0))
   (song::int (default 0))
   (songid::int (default 0))
   (songpos (default 0))
   (songlength::int (default 0))
   (bitrate::int (default 0))
   (khz::int (default 0))
   (err::obj (default #f)))
 |  musicstatusdenote that state of a 
player. | 
| 
| music-close music | bigloo multimedia procedure |  
| music-reset! music | bigloo multimedia procedure |  
Closes, resets, and tests the state of a music player.| music-closed? music | bigloo multimedia procedure |  | 
| 
| music-playlist-get music | bigloo multimedia procedure |  
| music-playlist-add! music song | bigloo multimedia procedure |  
| music-playlist-delete! music int | bigloo multimedia procedure |  
These functions controls the playlist used by a player.| music-playlist-clear! music | bigloo multimedia procedure |  
 Note: The
 songargument is an UTF8 encoded string (see
Section Unicode (UCS-2) Strings) whatever the local file
system encoding is. The functionmusic-playlist-getreturns a
list of UTF8 encoded names.
 
 music-playlist-get: returns the list of songs (UTF8 names) 
 of the current playlist.music-playlist-add!: adds an extra song (UTF8 name) at the end 
 of the playlist.music-delete!: removes the song numberintfrom the playlist.music-clear!: erases the whole playlist.
 | 
| 
| music-play music [song] | bigloo multimedia procedure |  
| music-seek music time [song] | bigloo multimedia procedure |  
| music-stop music | bigloo multimedia procedure |  
| music-pause music | bigloo multimedia procedure |  
| music-next music | bigloo multimedia procedure |  
These functions changes the state of the music player. The function| music-prev music | bigloo multimedia procedure |  music-seekseeks the playback position to the positiontime, 
which is an integer denoting a number of seconds. | 
| 
| music-crossfade music int | bigloo multimedia procedure |  
| music-random-set! music bool | bigloo multimedia procedure |  
These functions controls how songs playback should follow each other.| music-repeat-set! music bool | bigloo multimedia procedure |  | 
| 
| music-volume-get music | bigloo multimedia procedure |  
Get and set the audio volume of a player. Some player use the native mixer
supported by the operating system some others use a software mixer unrelated
to the hardware.| music-volume-set! music vol | bigloo multimedia procedure |  | 
| 
| music-status music | bigloo multimedia procedure |  
The function| music-update-status! music status | bigloo multimedia procedure |  music-statusreturns an instance of themusicstatusclass which denotes the state of the player. The functionmusic-update-status!updates this status. | 
| 
| music-song music | bigloo multimedia procedure |  
These two functions return the number of the song being played and the 
position in the song. These functions are somehow redundant with the
function| music-songpos music | bigloo multimedia procedure |  music-statusbecause the status also contains information
about the playback song and playback position. However, for some players
getting the music song and the playback position is cheaper than getting
the whole player status. | 
| 
Returns the metadata the current song.| music-meta music | bigloo multimedia procedure |  | 
| 
Reset the previous errors detected by a player.| music-reset-error! music | bigloo multimedia procedure |  | 
| 
The function| music-event-loop music [:onstate] [:onmeta] [:onerror] [:onvolume] | bigloo multimedia procedure |  music-event-loopenable event notifications when the state
of a player changes. The keyword arguments are:
 
 :onstate, a function of one parameter. When the player state 
changes, this function is called with an instance ofmusicstatusas first actual parameter.:onmeta, a function of two parameters. This function is
called when a metadata is detected in the music currently played.:onerror, a function of one parameter, invoked when an error
is detected.:onvolume, a function of one parameter, invoked when the volume
changes.
 | 
 
| 19.2.4 Music Player Daemon
 | 
Music Player Daemon (MPD in short) allows remote access for playing
music 
http://www.musicpd.org. MPD is designed for integrating a
computer into a stereo system that provides control for music playback
over a local network. The Bigloo class 
mpc implements a 
mpd
client. All Bigloo players can be access via the MPD protocol, using the
The following example shows how to access a MPlayer music player using the
MPD protocol with a simple Bigloo program:
| (module mpd
   (library multimedia pthread)
   (main main))
   
(define (main argv)
   (let ((db (instantiate::mpd-database
		(directories (cdr argv))))
	 (serv (make-server-socket 6600))
	 (music (instantiate::mplayer)))
      (let loop ()
	 (thread-start! (make-mpd-connection-thread music db sock))
	 (loop))))
 (define (make-mpd-connection-thread music db sock)
   (instantiate::pthread
      (body (lambda ()
	       (let ((pi (socket-input sock))
		     (po (socket-output sock)))
		  (input-timeout-set! pi 10000)
		  (output-timeout-set! po 10000)
		  (unwind-protect
		     (mpd music pi po db)
		     (socket-close sock)))))))
 | 
| 
The function| mpd music input-port output-port database [:log] | bigloo multimedia procedure |  mpdimplements a MPD server. It reads commands from theinput-portand write results tooutput-port. The argumentdatabase, an instance of thempd-databaseclass, describes the
music material that can be delivered by this player.
 
 | 
| 
| mpd-database | bigloo multimedia class |  
The field| (class mpd-database
   (directories::pair-nil read-only)
 |  directoriescontains the list of the directories that contains
music files. | 
 
 
The multimedia library provides functions for dealing with colors.
| 
| hsv->rgb h s v | bigloo multimedia procedure |  
| hsl->rgb h s l | bigloo multimedia procedure |  
| rgb-hsv r g b | bigloo multimedia procedure |  
These procedures converts from and to HSV, HSL, and RGB representations.
The argument| rgb-hsl r g b | bigloo multimedia procedure |  his an integer in the range[0..360], 
the argumentss,v, andlin the range[0..100]. The
argumentsr,g, andbare in the range[0..255].
These procedures returns multiple-values.
 
 
| (multiple-value-bind (r g b)
   (hsv->rgb 340 34 56)
   (list r g b)) => (143 94 110)
(multiple-value-bind (h s v)
   (rgb->hsv 255 0 0)
   (list h s v)) => (0 100 100)
 |  |