NAME
playlistfs – playlist file system

SYNOPSIS
games/playlistfs [ –s postname ] [ –m mountpoint ] [ –a ]

DESCRIPTION
Playlistfs implements an audio player which plays files from a built–in play list. The player is controlled through three files, usually mounted at /mnt. The files are /playctl for controlling play: start, stop, pause, skip, etc.; /playvol for controlling the playout volume; and /playlist for controlling the play list itself.

All three files can be written to control the player and read to obtain player status information.

When read, the files report the current status of the player, volume and playlist, respectively. End of file is indicated by a read that returns zero bytes, as usual. However, in all three files, subsequent read operations will block until the status of the file changes and then report the changed state. When the changed state has been read, another end–of–file indication is given, after which another read can be issued to wait for state changes.

The /playctl file returns strings of the form `cmd n' where cmd is one of stop, pause, or play and n is an index (or offset) into the playlist; indices start at zero.

The commands that can be written to /playctl take the same form; however, the index is an optional argument. If the index is omitted, the current value is used. The commands are play, stop, pause, resume, and skip. Play starts playing at the index. Stop stops playing. If an index is given, the current index is set to it and can be used in future commands. Pause and Resume interrupt and continue play, respectively. The index argument is always ignored and the whole command is ignored if the state in which they occur does not make sense. Skip adds the argument to the current index (adds one if no argument is given) and starts play at that index, stopping current play, if necessary.

Reads of /playvol return strings of the form `volume n', where n is a number or, if there is more than one channel, a quoted set of numbers, between 0 (minimum) and 100 (maximum). Writes to /playvol take the same form.

The /playlist file is an append–only file which accepts lines with one or two fields per line (parsed using tokenize). The first, compulsory, field is a file name, the optional second argument may contain a reference to, or a description of, the item, for instance in a graphical user interface. /playlist is append–only, individual lines cannot be removed. However, the playlist can be cleared by opening the file with the OTRUNC flag. A process that has /playlist open while the file is truncated will receive an error on the next read with errstr set to reading past eof. When this error occurs, clients can seek to the beginning of the file and reread its contents.

After starting up, Playlistfs puts itself in the background. When called with the –s flag, it posts a mountable file descriptor in /srv/playlist.postname. The –m flag can be used to specify a mount point other than /mnt.

Playlistfs uses the audio(1) decoders by running play(1) for format detection and conversion to pcm.

FILES
/srv/playlistfs.user: default playlistfs mountable file descriptor used by juke(7).
/mnt/playctl: Control file
/mnt/playlist: Playlist file
/mnt/playvol: Volume control file

SOURCE
/sys/src/games/music/playlistfs

SEE ALSO
play(1), audio(1), juke(7).