In the realm of audio CD & CD-ROM authoring on home computers, a cue sheet is a specially-formatted text file which relates an accompanying disc "image" (audio data file) with track boundaries and other non-audio data to be written to CD-R. Although it's possible to manually create a cue sheet in a text editor, CD ripping software typically generates a cue sheet as part of the ripping process, and then the cue sheet is used by CD burning software with no need for the user to ever see its contents.
Although intended for CD-R burning, cue sheets can also be used as playlists by some audio playing software and devices. They can also be used for mounting a ripped CD's files in a virtual (simulated) CD-ROM drive.
Relationship to CUETools
CUETools is multipurpose software for verifying and manipulating audio disc images (full-CD rips, not selected tracks), primarily via cue sheets. For example, given a cue sheet and audio image with all tracks in one file, CUETools can convert the rip to use a separate file for each track, perhaps with a different type of compression, and it will write a separate, converted cue sheet to match.
CUERipper is the DAE (Digital Audio Extraction, or "ripping") part of the CUETools package. It always writes a cue sheet when ripping.
The term "cue sheet" did not originate with home CD-R burning. Generally speaking, a cue sheet is a printed or handwritten list or schedule which denotes how a performance or block of media programming is divided; the times at which events or changes occur are typically "cues" for someone to invoke the intended event or change. There are different types of cue sheets for different purposes like radio programming, stage lighting, and professional authoring of optical discs (CD/DVD/Blu-Ray).
For example, in the early years of cinema, a type of cue sheet was sent to theatres along with silent movies, so that the local musicians providing musical accompaniment would know what kind of music to play, for how long, at what times. Radio stations have long used a type of cue sheet to log what they played and when, for reporting to collection/rights societies. Another type of cue sheet explains how sound recordings are to be arranged into a single multi-part program, such as for professional CD authoring—when a band wants to put together an album, they might supply a CD mastering engineer with a stack of CD-Rs or DATs containing the songs, along with a cue sheet telling the engineer, at a minimum, the intended order of the songs on the album. When assembling the album, the engineer then makes his own, more detailed cue sheet indicating specific track and sub-track boundaries, for use by whoever is making the glass master CD from which the production copies are manufactured.
Two types of cue sheets were developed to support CD burning.
The emergence of CD-ROM (data or mixed audio & data CDs), CD-R (recordable CDs) and CD "burners" (recorders) for the home and semi-pro market in the 1990s resulted in the advent, among other things, of the Disc-At-Once (DAO) recording mode, where all the CD-R's data is written in one burning session. To support optical disc authoring with these consumer devices, including the burning of CD-ROMs and audio CD-Rs in DAO mode, the SCSI ("scuzzy") standard for software communication with data storage devices was expanded to include various "multimedia commands" (MMC) for use by CD authoring/burning software. One such command allows the software to transmit a cue sheet before sending the main "program area" data (like the audio). This cue sheet tells the burner about the disc's "layout"—things like audio track boundaries and other info that would need to be written into the disc's "subcode", a set of ancillary data streams interleaved with the disc's main data, sync data, and error correction data.
The cue sheet needed by the SCSI "SEND CUE SHEET" command has a tightly packed binary data format, difficult to manually author. To make it easier for users, the author of two of the earliest burning programs, an MS-DOS program "DAO" (DAO.EXE) and its more full-featured counterpart for Windows (3.1/95/NT), "CDRWIN" (CDRWIN.EXE), created the BIN+CUE paradigm: the raw program-area data (the disc image) would be in one "BIN" file, and the cue sheet's info would be in a "CUE" text file with a more human-friendly format. This pair of files represents the entire CD.
The DAO/CDRWIN text-based format for cue sheets, despite having some flaws, is fairly simple and has become a de facto standard. The only spec for it is in the appendix of old versions of the CDRWIN user manual, although copies have been posted elsewhere on the Web. To date, no one has led an effort to improve upon the format, although the audio CD ripping/burning program Exact Audio Copy introduced a very popular "non-compliant" variation which enables the use of a cue sheet with a popular type of disc image (one-file-per-track, with gaps appended to previous track's file).
CUE or cue
BIN and CUE are not acronyms. In the MS-DOS and early Windows era, filenames were in 8.3 format: 1 to 8 alphanumeric characters for the main name, then a period, then 3 more alphanumeric characters for the filename "extension" denoting the type of content. For example, if a file was named README.TXT, it could be assumed to be a text file. Although these filenames could be referenced case-insensitively (like ReadMe.txt), they were normally stored and displayed by the OS in all-uppercase characters. By convention, people referred to different types of files by their uppercase filename extensions: TXT for generic text file, EXE for executable program, DOC for Microsoft Word document, etc.; so naturally, CUE was a text file in the DAO/CDRWIN cue sheet format. Even though Windows later supported and differentiated lowercase filenames, many people, including the authors of programs like Exact Audio Copy and CUETools, commonly refer to this type of cue sheet as a CUE, CUE sheet, CUE file, .CUE file, .cue file, .CUE, or .cue. They all mean the same thing; there's no wrong way of writing it.
- cue sheet at the Hydrogenaudio Knowledgebase - includes technical details and examples
- cue sheet (computing) at Wikipedia - less informative, but subject to more stringent editorial policies
- Cue-Sheet digitalx.org page at Internet Archive - a transcription of the "official" cue sheet format info from the CDRWIN documentation