path: root/Doc/library/cd.rst

:mod:`cd` --- CD-ROM access on SGI systems
==========================================

.. module:: cd
   :platform: IRIX
   :synopsis: Interface to the CD-ROM on Silicon Graphics systems.


This module provides an interface to the Silicon Graphics CD library. It is
available only on Silicon Graphics systems.

The way the library works is as follows.  A program opens the CD-ROM device with
:func:`open` and creates a parser to parse the data from the CD with
:func:`createparser`.  The object returned by :func:`open` can be used to read
data from the CD, but also to get status information for the CD-ROM device, and
to get information about the CD, such as the table of contents.  Data from the
CD is passed to the parser, which parses the frames, and calls any callback
functions that have previously been added.

An audio CD is divided into :dfn:`tracks` or :dfn:`programs` (the terms are used
interchangeably).  Tracks can be subdivided into :dfn:`indices`.  An audio CD
contains a :dfn:`table of contents` which gives the starts of the tracks on the
CD.  Index 0 is usually the pause before the start of a track.  The start of the
track as given by the table of contents is normally the start of index 1.

Positions on a CD can be represented in two ways.  Either a frame number or a
tuple of three values, minutes, seconds and frames.  Most functions use the
latter representation.  Positions can be both relative to the beginning of the
CD, and to the beginning of the track.

Module :mod:`cd` defines the following functions and constants:


.. function:: createparser()

   Create and return an opaque parser object.  The methods of the parser object are
   described below.


.. function:: msftoframe(minutes, seconds, frames)

   Converts a ``(minutes, seconds, frames)`` triple representing time in absolute
   time code into the corresponding CD frame number.


.. function:: open([device[, mode]])

   Open the CD-ROM device.  The return value is an opaque player object; methods of
   the player object are described below.  The device is the name of the SCSI
   device file, e.g. ``'/dev/scsi/sc0d4l0'``, or ``None``.  If omitted or ``None``,
   the hardware inventory is consulted to locate a CD-ROM drive.  The *mode*, if
   not omitted, should be the string ``'r'``.

The module defines the following variables:


.. exception:: error

   Exception raised on various errors.


.. data:: DATASIZE

   The size of one frame's worth of audio data.  This is the size of the audio data
   as passed to the callback of type ``audio``.


.. data:: BLOCKSIZE

   The size of one uninterpreted frame of audio data.

The following variables are states as returned by :func:`getstatus`:


.. data:: READY

   The drive is ready for operation loaded with an audio CD.


.. data:: NODISC

   The drive does not have a CD loaded.


.. data:: CDROM

   The drive is loaded with a CD-ROM.  Subsequent play or read operations will
   return I/O errors.


.. data:: ERROR

   An error occurred while trying to read the disc or its table of contents.


.. data:: PLAYING

   The drive is in CD player mode playing an audio CD through its audio jacks.


.. data:: PAUSED

   The drive is in CD layer mode with play paused.


.. data:: STILL

   The equivalent of :const:`PAUSED` on older (non 3301) model Toshiba CD-ROM
   drives.  Such drives have never been shipped by SGI.


.. data:: audio
          pnum
          index
          ptime
          atime
          catalog
          ident
          control

   Integer constants describing the various types of parser callbacks that can be
   set by the :meth:`addcallback` method of CD parser objects (see below).


.. _player-objects:

Player Objects
--------------

Player objects (returned by :func:`open`) have the following methods:


.. method:: CD player.allowremoval()

   Unlocks the eject button on the CD-ROM drive permitting the user to eject the
   caddy if desired.


.. method:: CD player.bestreadsize()

   Returns the best value to use for the *num_frames* parameter of the
   :meth:`readda` method.  Best is defined as the value that permits a continuous
   flow of data from the CD-ROM drive.


.. method:: CD player.close()

   Frees the resources associated with the player object.  After calling
   :meth:`close`, the methods of the object should no longer be used.


.. method:: CD player.eject()

   Ejects the caddy from the CD-ROM drive.


.. method:: CD player.getstatus()

   Returns information pertaining to the current state of the CD-ROM drive.  The
   returned information is a tuple with the following values: *state*, *track*,
   *rtime*, *atime*, *ttime*, *first*, *last*, *scsi_audio*, *cur_block*. *rtime*
   is the time relative to the start of the current track; *atime* is the time
   relative to the beginning of the disc; *ttime* is the total time on the disc.
   For more information on the meaning of the values, see the man page
   :manpage:`CDgetstatus(3dm)`. The value of *state* is one of the following:
   :const:`ERROR`, :const:`NODISC`, :const:`READY`, :const:`PLAYING`,
   :const:`PAUSED`, :const:`STILL`, or :const:`CDROM`.


.. method:: CD player.gettrackinfo(track)

   Returns information about the specified track.  The returned information is a
   tuple consisting of two elements, the start time of the track and the duration
   of the track.


.. method:: CD player.msftoblock(min, sec, frame)

   Converts a minutes, seconds, frames triple representing a time in absolute time
   code into the corresponding logical block number for the given CD-ROM drive.
   You should use :func:`msftoframe` rather than :meth:`msftoblock` for comparing
   times.  The logical block number differs from the frame number by an offset
   required by certain CD-ROM drives.


.. method:: CD player.play(start, play)

   Starts playback of an audio CD in the CD-ROM drive at the specified track.  The
   audio output appears on the CD-ROM drive's headphone and audio jacks (if
   fitted).  Play stops at the end of the disc. *start* is the number of the track
   at which to start playing the CD; if *play* is 0, the CD will be set to an
   initial paused state.  The method :meth:`togglepause` can then be used to
   commence play.


.. method:: CD player.playabs(minutes, seconds, frames, play)

   Like :meth:`play`, except that the start is given in minutes, seconds, and
   frames instead of a track number.


.. method:: CD player.playtrack(start, play)

   Like :meth:`play`, except that playing stops at the end of the track.


.. method:: CD player.playtrackabs(track, minutes, seconds, frames, play)

   Like :meth:`play`, except that playing begins at the specified absolute time and
   ends at the end of the specified track.


.. method:: CD player.preventremoval()

   Locks the eject button on the CD-ROM drive thus preventing the user from
   arbitrarily ejecting the caddy.


.. method:: CD player.readda(num_frames)

   Reads the specified number of frames from an audio CD mounted in the CD-ROM
   drive.  The return value is a string representing the audio frames.  This string
   can be passed unaltered to the :meth:`parseframe` method of the parser object.


.. method:: CD player.seek(minutes, seconds, frames)

   Sets the pointer that indicates the starting point of the next read of digital
   audio data from a CD-ROM.  The pointer is set to an absolute time code location
   specified in *minutes*, *seconds*, and *frames*.  The return value is the
   logical block number to which the pointer has been set.


.. method:: CD player.seekblock(block)

   Sets the pointer that indicates the starting point of the next read of digital
   audio data from a CD-ROM.  The pointer is set to the specified logical block
   number.  The return value is the logical block number to which the pointer has
   been set.


.. method:: CD player.seektrack(track)

   Sets the pointer that indicates the starting point of the next read of digital
   audio data from a CD-ROM.  The pointer is set to the specified track.  The
   return value is the logical block number to which the pointer has been set.


.. method:: CD player.stop()

   Stops the current playing operation.


.. method:: CD player.togglepause()

   Pauses the CD if it is playing, and makes it play if it is paused.


.. _cd-parser-objects:

Parser Objects
--------------

Parser objects (returned by :func:`createparser`) have the following methods:


.. method:: CD parser.addcallback(type, func, arg)

   Adds a callback for the parser.  The parser has callbacks for eight different
   types of data in the digital audio data stream.  Constants for these types are
   defined at the :mod:`cd` module level (see above). The callback is called as
   follows: ``func(arg, type, data)``, where *arg* is the user supplied argument,
   *type* is the particular type of callback, and *data* is the data returned for
   this *type* of callback.  The type of the data depends on the *type* of callback
   as follows:

   +-------------+---------------------------------------------+
   | Type        | Value                                       |
   +=============+=============================================+
   | ``audio``   | String which can be passed unmodified to    |
   |             | :func:`al.writesamps`.                      |
   +-------------+---------------------------------------------+
   | ``pnum``    | Integer giving the program (track) number.  |
   +-------------+---------------------------------------------+
   | ``index``   | Integer giving the index number.            |
   +-------------+---------------------------------------------+
   | ``ptime``   | Tuple consisting of the program time in     |
   |             | minutes, seconds, and frames.               |
   +-------------+---------------------------------------------+
   | ``atime``   | Tuple consisting of the absolute time in    |
   |             | minutes, seconds, and frames.               |
   +-------------+---------------------------------------------+
   | ``catalog`` | String of 13 characters, giving the catalog |
   |             | number of the CD.                           |
   +-------------+---------------------------------------------+
   | ``ident``   | String of 12 characters, giving the ISRC    |
   |             | identification number of the recording.     |
   |             | The string consists of two characters       |
   |             | country code, three characters owner code,  |
   |             | two characters giving the year, and five    |
   |             | characters giving a serial number.          |
   +-------------+---------------------------------------------+
   | ``control`` | Integer giving the control bits from the CD |
   |             | subcode data                                |
   +-------------+---------------------------------------------+


.. method:: CD parser.deleteparser()

   Deletes the parser and frees the memory it was using.  The object should not be
   used after this call.  This call is done automatically when the last reference
   to the object is removed.


.. method:: CD parser.parseframe(frame)

   Parses one or more frames of digital audio data from a CD such as returned by
   :meth:`readda`.  It determines which subcodes are present in the data.  If these
   subcodes have changed since the last frame, then :meth:`parseframe` executes a
   callback of the appropriate type passing to it the subcode data found in the
   frame. Unlike the C function, more than one frame of digital audio data can be
   passed to this method.


.. method:: CD parser.removecallback(type)

   Removes the callback for the given *type*.


.. method:: CD parser.resetparser()

   Resets the fields of the parser used for tracking subcodes to an initial state.
   :meth:`resetparser` should be called after the disc has been changed.