304 lines
11 KiB
TeX
304 lines
11 KiB
TeX
\section{\module{cd} ---
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CD-ROM access on SGI systems}
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\declaremodule{builtin}{cd}
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\modulesynopsis{Interface to the CD-ROM on Silicon Graphics systems.}
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This module provides an interface to the Silicon Graphics CD library.
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It is available only on Silicon Graphics systems.
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The way the library works is as follows. A program opens the CD-ROM
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device with \function{open()} and creates a parser to parse the data
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from the CD with \function{createparser()}. The object returned by
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\function{open()} can be used to read data from the CD, but also to get
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status information for the CD-ROM device, and to get information about
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the CD, such as the table of contents. Data from the CD is passed to
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the parser, which parses the frames, and calls any callback
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functions that have previously been added.
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An audio CD is divided into \dfn{tracks} or \dfn{programs} (the terms
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are used interchangeably). Tracks can be subdivided into
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\dfn{indices}. An audio CD contains a \dfn{table of contents} which
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gives the starts of the tracks on the CD. Index 0 is usually the
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pause before the start of a track. The start of the track as given by
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the table of contents is normally the start of index 1.
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Positions on a CD can be represented in two ways. Either a frame
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number or a tuple of three values, minutes, seconds and frames. Most
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functions use the latter representation. Positions can be both
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relative to the beginning of the CD, and to the beginning of the
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track.
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Module \module{cd} defines the following functions and constants:
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\begin{funcdesc}{createparser}{}
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Create and return an opaque parser object. The methods of the parser
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object are described below.
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\end{funcdesc}
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\begin{funcdesc}{msftoframe}{minutes, seconds, frames}
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Converts a \code{(\var{minutes}, \var{seconds}, \var{frames})} triple
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representing time in absolute time code into the corresponding CD
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frame number.
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\end{funcdesc}
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\begin{funcdesc}{open}{\optional{device\optional{, mode}}}
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Open the CD-ROM device. The return value is an opaque player object;
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methods of the player object are described below. The device is the
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name of the SCSI device file, e.g. \code{'/dev/scsi/sc0d4l0'}, or
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\code{None}. If omitted or \code{None}, the hardware inventory is
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consulted to locate a CD-ROM drive. The \var{mode}, if not omited,
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should be the string \code{'r'}.
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\end{funcdesc}
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The module defines the following variables:
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\begin{excdesc}{error}
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Exception raised on various errors.
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\end{excdesc}
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\begin{datadesc}{DATASIZE}
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The size of one frame's worth of audio data. This is the size of the
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audio data as passed to the callback of type \code{audio}.
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\end{datadesc}
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\begin{datadesc}{BLOCKSIZE}
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The size of one uninterpreted frame of audio data.
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\end{datadesc}
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The following variables are states as returned by
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\function{getstatus()}:
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\begin{datadesc}{READY}
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The drive is ready for operation loaded with an audio CD.
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\end{datadesc}
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\begin{datadesc}{NODISC}
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The drive does not have a CD loaded.
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\end{datadesc}
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\begin{datadesc}{CDROM}
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The drive is loaded with a CD-ROM. Subsequent play or read operations
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will return I/O errors.
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\end{datadesc}
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\begin{datadesc}{ERROR}
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An error aoocurred while trying to read the disc or its table of
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contents.
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\end{datadesc}
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\begin{datadesc}{PLAYING}
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The drive is in CD player mode playing an audio CD through its audio
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jacks.
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\end{datadesc}
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\begin{datadesc}{PAUSED}
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The drive is in CD layer mode with play paused.
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\end{datadesc}
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\begin{datadesc}{STILL}
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The equivalent of \constant{PAUSED} on older (non 3301) model Toshiba
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CD-ROM drives. Such drives have never been shipped by SGI.
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\end{datadesc}
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\begin{datadesc}{audio}
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\dataline{pnum}
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\dataline{index}
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\dataline{ptime}
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\dataline{atime}
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\dataline{catalog}
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\dataline{ident}
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\dataline{control}
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Integer constants describing the various types of parser callbacks
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that can be set by the \method{addcallback()} method of CD parser
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objects (see below).
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\end{datadesc}
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\subsection{Player Objects}
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\label{player-objects}
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Player objects (returned by \function{open()}) have the following
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methods:
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\begin{methoddesc}[CD player]{allowremoval}{}
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Unlocks the eject button on the CD-ROM drive permitting the user to
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eject the caddy if desired.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{bestreadsize}{}
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Returns the best value to use for the \var{num_frames} parameter of
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the \method{readda()} method. Best is defined as the value that
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permits a continuous flow of data from the CD-ROM drive.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{close}{}
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Frees the resources associated with the player object. After calling
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\method{close()}, the methods of the object should no longer be used.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{eject}{}
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Ejects the caddy from the CD-ROM drive.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{getstatus}{}
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Returns information pertaining to the current state of the CD-ROM
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drive. The returned information is a tuple with the following values:
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\var{state}, \var{track}, \var{rtime}, \var{atime}, \var{ttime},
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\var{first}, \var{last}, \var{scsi_audio}, \var{cur_block}.
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\var{rtime} is the time relative to the start of the current track;
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\var{atime} is the time relative to the beginning of the disc;
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\var{ttime} is the total time on the disc. For more information on
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the meaning of the values, see the man page \manpage{CDgetstatus}{3dm}.
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The value of \var{state} is one of the following: \constant{ERROR},
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\constant{NODISC}, \constant{READY}, \constant{PLAYING},
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\constant{PAUSED}, \constant{STILL}, or \constant{CDROM}.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{gettrackinfo}{track}
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Returns information about the specified track. The returned
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information is a tuple consisting of two elements, the start time of
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the track and the duration of the track.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{msftoblock}{min, sec, frame}
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Converts a minutes, seconds, frames triple representing a time in
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absolute time code into the corresponding logical block number for the
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given CD-ROM drive. You should use \function{msftoframe()} rather than
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\method{msftoblock()} for comparing times. The logical block number
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differs from the frame number by an offset required by certain CD-ROM
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drives.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{play}{start, play}
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Starts playback of an audio CD in the CD-ROM drive at the specified
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track. The audio output appears on the CD-ROM drive's headphone and
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audio jacks (if fitted). Play stops at the end of the disc.
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\var{start} is the number of the track at which to start playing the
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CD; if \var{play} is 0, the CD will be set to an initial paused
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state. The method \method{togglepause()} can then be used to commence
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play.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{playabs}{minutes, seconds, frames, play}
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Like \method{play()}, except that the start is given in minutes,
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seconds, and frames instead of a track number.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{playtrack}{start, play}
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Like \method{play()}, except that playing stops at the end of the
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track.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{playtrackabs}{track, minutes, seconds, frames, play}
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Like \method{play()}, except that playing begins at the spcified
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absolute time and ends at the end of the specified track.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{preventremoval}{}
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Locks the eject button on the CD-ROM drive thus preventing the user
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from arbitrarily ejecting the caddy.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{readda}{num_frames}
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Reads the specified number of frames from an audio CD mounted in the
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CD-ROM drive. The return value is a string representing the audio
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frames. This string can be passed unaltered to the
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\method{parseframe()} method of the parser object.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{seek}{minutes, seconds, frames}
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Sets the pointer that indicates the starting point of the next read of
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digital audio data from a CD-ROM. The pointer is set to an absolute
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time code location specified in \var{minutes}, \var{seconds}, and
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\var{frames}. The return value is the logical block number to which
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the pointer has been set.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{seekblock}{block}
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Sets the pointer that indicates the starting point of the next read of
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digital audio data from a CD-ROM. The pointer is set to the specified
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logical block number. The return value is the logical block number to
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which the pointer has been set.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{seektrack}{track}
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Sets the pointer that indicates the starting point of the next read of
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digital audio data from a CD-ROM. The pointer is set to the specified
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track. The return value is the logical block number to which the
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pointer has been set.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{stop}{}
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Stops the current playing operation.
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\end{methoddesc}
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\begin{methoddesc}[CD player]{togglepause}{}
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Pauses the CD if it is playing, and makes it play if it is paused.
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\end{methoddesc}
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\subsection{Parser Objects}
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\label{cd-parser-objects}
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Parser objects (returned by \function{createparser()}) have the
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following methods:
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\begin{methoddesc}[CD parser]{addcallback}{type, func, arg}
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Adds a callback for the parser. The parser has callbacks for eight
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different types of data in the digital audio data stream. Constants
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for these types are defined at the \module{cd} module level (see above).
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The callback is called as follows: \code{\var{func}(\var{arg}, type,
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data)}, where \var{arg} is the user supplied argument, \var{type} is
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the particular type of callback, and \var{data} is the data returned
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for this \var{type} of callback. The type of the data depends on the
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\var{type} of callback as follows:
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\begin{tableii}{l|p{4in}}{code}{Type}{Value}
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\lineii{audio}{String which can be passed unmodified to
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\function{al.writesamps()}.}
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\lineii{pnum}{Integer giving the program (track) number.}
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\lineii{index}{Integer giving the index number.}
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\lineii{ptime}{Tuple consisting of the program time in minutes,
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seconds, and frames.}
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\lineii{atime}{Tuple consisting of the absolute time in minutes,
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seconds, and frames.}
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\lineii{catalog}{String of 13 characters, giving the catalog number
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of the CD.}
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\lineii{ident}{String of 12 characters, giving the ISRC
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identification number of the recording. The string consists of two
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characters country code, three characters owner code, two characters
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giving the year, and five characters giving a serial number.}
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\lineii{control}{Integer giving the control bits from the CD
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subcode data}
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\end{tableii}
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\end{methoddesc}
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\begin{methoddesc}[CD parser]{deleteparser}{}
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Deletes the parser and frees the memory it was using. The object
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should not be used after this call. This call is done automatically
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when the last reference to the object is removed.
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\end{methoddesc}
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\begin{methoddesc}[CD parser]{parseframe}{frame}
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Parses one or more frames of digital audio data from a CD such as
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returned by \method{readda()}. It determines which subcodes are
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present in the data. If these subcodes have changed since the last
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frame, then \method{parseframe()} executes a callback of the
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appropriate type passing to it the subcode data found in the frame.
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Unlike the \C{} function, more than one frame of digital audio data
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can be passed to this method.
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\end{methoddesc}
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\begin{methoddesc}[CD parser]{removecallback}{type}
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Removes the callback for the given \var{type}.
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\end{methoddesc}
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\begin{methoddesc}[CD parser]{resetparser}{}
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Resets the fields of the parser used for tracking subcodes to an
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initial state. \method{resetparser()} should be called after the disc
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has been changed.
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\end{methoddesc}
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