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))))))
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The multimedia library provides functions for accessing the metadata
generated by digital camera.
| jpeg-exif file-name | Bigloo Multimedia procedure |
The function jpeg-exif extracts the EXIF
(http://en.wikipedia.org/wiki/Exif) metadata of a JPEG file as created
by digital camera. The argument file-name is the name of the JPEG
file. If the file contains an EXIF section it is returned as an instance
of the exif class. Otherwise, this function returns #f.
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| jpeg-exif-comment-set! file-name text | Bigloo Multimedia procedure |
Set the comment of the EXIF metadata section of the file file-name
to text.
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| exif | Bigloo Multimedia class |
(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)))
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The instance of the exif class maps the EXIF metadata found in JPEG
files into Bigloo objects. Since all fields are optional they are untyped.
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| exif-date->date | Bigloo Multimedia procedure |
Parses an exif date, i.e., a string of characters, and returns
corresponding date. Raises an &io-parse-error if 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]
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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
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| read-m3u input-port | Bigloo Multimedia procedure |
| write-m3u list output-port | Bigloo Multimedia procedure |
The function read-m3u reads a playlist expressed in the M3U
format from input-port and returns a list of songs. The function
write-m3u encode such a list encoded in the M3U format to an
output port.
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| file-musictag file-name | Bigloo Multimedia procedure |
| mp3-musictag file-name | Bigloo Multimedia procedure |
| ogg-musictag file-name | Bigloo Multimedia procedure |
| flac-musictag file-name | Bigloo Multimedia procedure |
These functions extract the metadata of a music file named file-name.
The function mp3-musictag returns the ID3 tag section if it
exists. Otherwise, it returns #f. The function ogg-musictag
and flac-musictag returns the vorbis comment if it exists.
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| musictag | Bigloo Multimedia class |
(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)))
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This class is used as the base class of music tag formats.
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| id3::musictag | Bigloo Multimedia class |
(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)))
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This class is used to reify the ID3 metadata used in the MP3 format.
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| vorbis::musictag | Bigloo Multimedia class |
This class is used to reify the Vorbis comments of OGG and Flac files.
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Bigloo proposes various functions and classes for controlling the
audio volume of sound cards.
| mixer | Bigloo Multimedia class |
(class mixer
(devices::pair-nil (default '())))
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The field devices is a list of available channels.
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| mixer-close mix | Bigloo Multimedia procedure |
Closes a mixer. The argument mix must be an instance of
the mixer class.
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| mixer-volume-get mix channel | Bigloo Multimedia procedure |
| mixer-volume-set! mix channel leftv rightv | Bigloo Multimedia procedure |
The function mixer-volume-get returns the left and right volume
levels (two values) of the channel of the mixer mix. The
channel is denoted by its name and is represented as a string of
characters. The argument mix is an instance of the mixer class.
The function mixer-volume-set! changes the audio level of a mixer
channel.
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| soundcard::mixer | Bigloo Multimedia class |
(class soundcard::mixer
(device::bstring read-only))
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The instances of the class soundcard, a subclass of the
mixer class, are used to access physical soundcard as supported
by operating systems. The class field device stands 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.
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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))))))
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| music | Bigloo Multimedia abstract class |
(abstract-class music
(frequency::long (default 2000000))
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This abstract class is the root class of all music players.
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| musicproc::music | Bigloo Multimedia class |
(class musicproc::music
(charset::symbol (default 'ISO-LATIN-1)))
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This class is used to reify player that are run in an external process.
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| mplayer::musicproc | Bigloo Multimedia class |
(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)))
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A player based on the external software MPlayer. Creating such a player
spawns in background a MPlayer process.
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| mpg123::musicproc | Bigloo Multimedia class |
(class mpg123::musicproc
(path::bstring read-only (default "mpg123"))
(args::pair-nil read-only (default '("--remote"))))
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A player based on the external software mpg123.
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| mpc::music | Bigloo Multimedia class |
(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)))
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A MPC client.
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. The prefix field allows
programmer to write portable code that manages play list file names
independently of the player selected.
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| musicstatus | Bigloo Multimedia 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)))
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The instances of the class musicstatus denote that state of a
player.
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| music-close music | Bigloo Multimedia procedure |
| music-reset! music | Bigloo Multimedia procedure |
| music-closed? music | Bigloo Multimedia procedure |
Closes, resets, and tests the state of a music player.
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| music-playlist-get music | Bigloo Multimedia procedure |
| music-playlist-add! music song | Bigloo Multimedia procedure |
| music-playlist-delete! music int | Bigloo Multimedia procedure |
| music-playlist-clear! music | Bigloo Multimedia procedure |
These functions controls the playlist used by a player.
Note: The song argument is an UTF8 encoded string (see
Section Unicode (UCS-2) Strings) whatever the local file
system encoding is. The function music-playlist-get returns 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 number int from the playlist.
music-clear!: erases the whole playlist.
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| 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 |
| music-prev music | Bigloo Multimedia procedure |
These functions changes the state of the music player. The function
music-seek seeks the playback position to the position time,
which is an integer denoting a number of seconds.
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| music-crossfade music int | Bigloo Multimedia procedure |
| music-random-set! music bool | Bigloo Multimedia procedure |
| music-repeat-set! music bool | Bigloo Multimedia procedure |
These functions controls how songs playback should follow each other.
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| music-volume-get music | Bigloo Multimedia procedure |
| music-volume-set! music vol | 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.
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| music-status music | Bigloo Multimedia procedure |
| music-update-status! music status | Bigloo Multimedia procedure |
The function music-status returns an instance of the musicstatus
class which denotes the state of the player. The function
music-update-status! updates this status.
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| music-song music | Bigloo Multimedia procedure |
| music-songpos 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-status because 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.
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| music-meta music | Bigloo Multimedia procedure |
Returns the metadata the current song.
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| music-reset-error! music | Bigloo Multimedia procedure |
Reset the previous errors detected by a player.
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| music-event-loop music [:onstate] [:onmeta] [:onerror] [:onvolume] | Bigloo Multimedia procedure |
The function music-event-loop enable 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 of musicstatus
as 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.
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19.2.4 Music Player Daemon
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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)))))))
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| mpd music input-port output-port database [:log] | Bigloo Multimedia procedure |
The function mpd implements a MPD server. It reads commands from the
input-port and write results to output-port. The argument
database, an instance of the mpd-database class, describes the
music material that can be delivered by this player.
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| mpd-database | Bigloo Multimedia class |
(class mpd-database
(directories::pair-nil read-only)
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The field directories contains the list of the directories that contains
music files.
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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 |
| rgb-hsl r g b | Bigloo Multimedia procedure |
These procedures converts from and to HSV, HSL, and RGB representations.
The argument h is an integer in the range [0..360],
the arguments s, v, and l in the range [0..100]. The
arguments r, g, and b are 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)
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