39.3. cd — CD-ROM access on SGI systems

Obsoleto desde a versão 2.6: The cd module has been removed in Python 3.

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 open() and creates a parser to parse the data from the CD with createparser(). The object returned by 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 tracks or programs (the terms are used interchangeably). Tracks can be subdivided into indices. An audio CD contains a 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 cd defines the following functions and constants:

cd.createparser()

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

cd.msftoframe(minutes, seconds, frames)

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

cd.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 cd.error

Exception raised on various errors.

cd.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.

cd.BLOCKSIZE

The size of one uninterpreted frame of audio data.

The following variables are states as returned by getstatus():

cd.READY

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

cd.NODISC

The drive does not have a CD loaded.

cd.CDROM

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

cd.ERROR

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

cd.PLAYING

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

cd.PAUSED

The drive is in CD layer mode with play paused.

cd.STILL

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

cd.audio

cd.pnum

cd.index

cd.ptime

cd.atime

cd.catalog

cd.ident

cd.control

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

39.3.1. Player Objects

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

CD player.allowremoval()

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

CD player.bestreadsize()

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

CD player.close()

Frees the resources associated with the player object. After calling close(), the methods of the object should no longer be used.

CD player.eject()

Ejects the caddy from the CD-ROM drive.

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 CDgetstatus(3dm). The value of state is one of the following: ERROR, NODISC, READY, PLAYING, PAUSED, STILL, or CDROM.

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.

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 msftoframe() rather than msftoblock() for comparing times. The logical block number differs from the frame number by an offset required by certain CD-ROM drives.

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 togglepause() can then be used to commence play.

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

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

CD player.playtrack(start, play)

Like play(), except that playing stops at the end of the track.

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

Like play(), except that playing begins at the specified absolute time and ends at the end of the specified track.

CD player.preventremoval()

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

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 parseframe() method of the parser object.

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.

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.

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.

CD player.stop()

Stops the current playing operation.

CD player.togglepause()

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

39.3.2. Parser Objects

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

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 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:

Tipo	Valor
audio	String which can be passed unmodified to 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

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.

CD parser.parseframe(frame)

Parses one or more frames of digital audio data from a CD such as returned by readda(). It determines which subcodes are present in the data. If these subcodes have changed since the last frame, then 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.

CD parser.removecallback(type)

Removes the callback for the given type.

CD parser.resetparser()

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