Compressed audio optical disc
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A compressed audio optical disc, MP3 CD, or MP3 CD-ROM or MP3 DVD is an
optical disc In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces. ...
(usually a
CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the i ...
,
CD-RW CD-RW (Compact Disc-Rewritable) is a digital optical disc storage format introduced in 1997. A CD-RW compact disc (CD-RWs) can be written, read, erased, and re-written. CD-RWs, as opposed to CDs, require specialized readers that have sensi ...
, DVD-R or
DVD-RW DVD recordable and DVD rewritable are optical disc recording technologies. Both terms describe DVD optical discs that can be written to by a DVD recorder, whereas only 'rewritable' discs are able to erase and rewrite data. Data is written ('bur ...
) that contains digital audio in the
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Origin ...
file format. Discs are
written Writing is a medium of human communication which involves the representation of a language through a system of physically inscribed, mechanically transferred, or digitally represented symbols. Writing systems do not themselves constitute h ...
in the "Yellow Book" standard data format (used for CD-ROMs and
DVD-ROM The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
s), as opposed to the Red Book standard audio format (used for
CD-DA Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named ...
audio CDs).


Description

Compressed to audio files are supported by many modern
CD player A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982. CDs typically contain recordings of audio material such as music or audio ...
s as well as
DVD player A DVD player is a device that plays DVDs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. Some DVD players will also play audio CDs. DVD players are connected to a television to ...
s. Disc players are capable of playing compressed formats, such as MP3, the most commonly used format, as well as
Ogg Vorbis Vorbis is a free and open-source software project headed by the Xiph.Org Foundation. The project produces an audio coding format and software reference encoder/decoder (codec) for lossy audio compression. Vorbis is most commonly used in conjun ...
, the proprietary
Windows Media Audio Windows Media Audio (WMA) is a series of audio codecs and their corresponding audio coding formats developed by Microsoft. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The ...
and ATRAC. Because of
audio data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...
, optical discs do not have to spin all of the time, potentially saving
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
power; however, decompressing the audio takes more processor time. The audio is
buffer Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Buffering agent, the weak acid or base in a buffer solution * Lysis buffer, in cell biology * Metal ion buffer * ...
ed in
random-access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the ...
, which also provides protection against skipping. The number of files that a disc can hold depends on how the audio files are encoded and the length of the audio. A standard audio CD (74 minutes) can hold about 18 audio programs, a 650- MB data CD (equivalent to 74-minute audio CD) containing mid-quality (160-
kb/s In telecommunications, data-transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...
) audio files can hold approximately 9.5 hours of audio or about 138 audio tracks.
ID3 ID3 is a metadata container most often used in conjunction with the MP3 audio file format. It allows information such as the title, artist, album, track number, and other information about the file to be stored in the file itself. There are tw ...
tags stored in compressed audio files can be displayed by some players, and some players can search for audio files within directories on a compressed audio optical disc. There is no official standard for how audio files on a compressed audio optical CD are stored on discs. As such, the format expected by different players varies. This sometimes leads to incompatibilities and difficulty in playing discs, often because of filename length limits, sub-directory limits, number of files limits, and special character bugs. Sometimes, pressed CDs containing MP3s can be used, since some CD-ROM video games can act as an "MP3 CD" for some users. Some older classic CD-ROM games tend to use
WAV Waveform Audio File Format (WAVE, or WAV due to its filename extension; pronounced "wave") is an audio file format standard, developed by IBM and Microsoft, for storing an audio bitstream on PCs. It is the main format used on Microsoft Wind ...
files since WAV files were the biggest audio format throughout the 90s, in which WAV files on optical discs are also compatible with CD players which have Yellow Book CD-ROM support.


Use in audiobooks

This technology is most commonly used in audiobooks new on CD since 2000 or so. Especially since unabridged audiobooks can run into many hours length. CEA/APA has published the following standards on audiobooks. *CEA-2003-C - Digital Audiobook File Format and Player Requirements *CEA-2004, Audiobook Media and Player Compatibility.


Advantages compared to Red Book audio CDs

*longer runtime as per file compression **6 red book audio discs for the price of one Yellow Book (CD-ROM), depending on file compression rates *Longer battery life from fewer disc spins *Discs marketed without "music" endorsement aren't rejected since Yellow Book mode (CD-ROM) is being used instead of Red Book audio mode.


Disadvantages compared to other means to play compressed digital audio

Most disadvantages with compressed audio optical discs are present with CDs, and DVDs in general.


Re-write (RW) limits and compatibility compared to write-once (R)

Compared to solid-state flash memory which can be rewritten a finite amount of about 100,000 times and
hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
s which can be rewritten a near-infinite number of times, optical discs with compressed audio on them are either non-rewritable (
CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the i ...
/ DVD-R), or can only be rewritten about 1000 times, which includes having to erase the entire volume before re-writing (
CD-RW CD-RW (Compact Disc-Rewritable) is a digital optical disc storage format introduced in 1997. A CD-RW compact disc (CD-RWs) can be written, read, erased, and re-written. CD-RWs, as opposed to CDs, require specialized readers that have sensi ...
/
DVD-RW DVD recordable and DVD rewritable are optical disc recording technologies. Both terms describe DVD optical discs that can be written to by a DVD recorder, whereas only 'rewritable' discs are able to erase and rewrite data. Data is written ('bur ...
). In some cases 1000 write/erase cycles (including entire volume erasure per re-write) on RW optical discs vs. 100,000+ write/erase cycles on flash memory (while retaining old data) can be somewhat of a moot point with applications that have less demand for usage. Another issue re-writable optical discs suffer from, is that the re-writable discs have less compatibility with older disc players, though most CD and DVD players that support MP3s and other compressed audio will support RW discs easily.


Longevity of service life

The dependency of moving parts for the associated equipment guarantees less runtime than solid-state portable media players for battery life reasons, as well as the overall service life. When being looped, an optical disc player can fail in less than one month when spinning uninterrupted, and solid-state portable media players can run for as long as 6 months uninterrupted without failure.


Shelf space

Yellow Book optical disc ROMs with compressed audio may free up as many as five Red Book audio CDs, but they still demand much shelf space, compared to external hard drives and solid-state flash memory.


Material degradation

Unlike mechanical disks with permanent housing such as
hard drives A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
, and solid-state devices like flash memory which generally has inexpensive but tough housing, optical discs typically have a reflective surface that can get damaged at relatively low thresholds of surface damage, in which if damage is just accidental, it could mean rendering it unusable. Also, the repeated handling of discs between jewel case and disc drive exposes the disc to dust, and also makes the disc liable to be damaged permanently. Also note that some CD and DVD discs also have defective aluminum layers that can flake, and damage the disc naturally. If an archival-grade disc is used, such as
gold CD A gold compact disc is one in which gold is used in place of the super pure aluminium commonly used as the reflective coating on ordinary CDs or silver on ordinary CD-Rs. Gold CDs can be played in any CD player. Blank gold CD-Rs are also availab ...
or
M-DISC M-DISC (Millennial Disc) is a write-once optical disc technology introduced in 2009 by Millenniata, Inc.and available as DVD and Blu-ray discs. Overview M-DISC's design is intended to provide archival media longevity.M-Disc claims that prop ...
, the disc can last far longer than hard drives or flash memory.


File/volume size limits and access to files

Repeated insertion and removal of optical discs can occur when somebody has to deal with multi-gigabyte collections which can span across as many as 10 CD-Rs (or 5 DVD-Rs) or even more when lots more gigabytes were to be used. Sometimes when somebody is looking for a specific MP3 or similar; it can result in insertion and removal if more discs were used to increase the size of a library of files, in which copying the files to a hard drive, and archiving them there can be a workaround to ensure faster access to files. Recordable Blu-ray Discs can somewhat solve this problem, but they too suffer from most other disadvantages. The high cost of stand-alone Blu-ray burners, as well as the higher cost of equipment with BD-ROM drives can negate buying sold-state flash memory instead, of which the re-writability of flash memory also negates Blu-ray's apparent advantages.


See also

* Red Book:
Compact Disc Digital Audio Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named ...
(CD-DA) * Yellow Book: Compact Disc Read-Only Memory ( CD-ROM)


References

{{Reflist MP3 Compact disc DVD