Sustainability of Digital Formats: Planning for Library of Congress Collections

DDP, short for Disc Description Protocol (also sometimes called DDPi for DDP Image) is a proprietary method that identifies, organizes and describes a specific set of data recorded onto a DVD or CD optical disc. Although there is no publicly available specification (see Documentation below), it is considered the standard delivery format for CD and DVD replication, according to many sources including Sony Music. DDP was invented by Doug Carson of DCA (link via Internet Archive) and was trademarked by Doug Carson & Associates, Inc. in March 2004. See History for information about versions. Note that DDP is not a file format per se in that it's not defined by a single file extension or Media Type but rather, DDP is more of a disc image of the CD (or DVD) content. Its inclusion, starting in 2024, as an acceptable format for Audio - Media-independent (digital) in the Library's Recommended Formats Statement brings it to this resource.

Structurally, a DDP is a set of required and optional files and their exact composition within the set is variable. It can be as few as three or four components or as many as eight or more. The DDP set is packaged typically as a ZIP file or another aggregate format such as RAR or 7z. According to Francis Rumsey in Desktop Audio Technology: Digital Audio and MIDI Principles (excerpts are available online through Google Books - see p. 185-186), DDPs are comprised of "a number of streams of data, each of which carries different information to describe the contents of the disc. These streams may be either a series of packets or data transferred over a network, files on a disc or tape, or raw blocks of data independent of any filing system. The DDP protocol simply maps it data into whatever blocks or packets size used by the media concerned, provided that the block or packet size is at least 128 bytes." The typical components or streams in a DDP are:

• DDPID: the identifier of the disc which is 128 bytes long, "depending on the type and level of DDP information, various 'vital statistics' about the other DDP files and their location on the medium, ... and a user text field (not transferred to the CD)"
• DDPMS or DDP Map Stream (also referred to the DDP Stream Descriptor) which, according to Rumsey, "is a stream of 128-byte data packets which together give a map of the CD contents, showing what types of CD data are to be recorded in each part of the CD, how long the streams are, what types of subcode are included, and so forth. Pointers are included to the relevant text, subcode and main streams (or files) for each part of the CD."
• Text stream: "optional stream containing text to describe the titling information for volumes, tracks or index points or for other text comments. If stored as a file [usually with the .txt extension], its name is indicated in the appropriate map pocket."
• DDPPQ or PQDESCR: optional subcode descriptor which "contains information about the subcode data to be included within part of the disc, particularly for CD-DA. If stored as a file, its name is indicated in the appropriate map pocket." its name is indicated in the appropriate map pocket."    
• Main stream or track file: Contains the actual audio data for the DDP, "treated simply as a stream of bytes."
• Comments welcome.

For a sample DDP template, see Music Guy Mastering DDP Template.

As BluePro Mastering states, DDP have advantages including data integrity ("DDP files are not subject to manipulation and end up exactly as the artist intended. An audio CDR, for example, can influence the sound of a recording when used as a master due to errors and other effects of different dyes used in the disc itself"), increased delivery speed ("DDP can be transferred using any medium including over the internet which speeds up the production process"), and lack of replication errors (due to inclusion of MD5 fixity value).

The Library of Congress has a small number of DDP files, especially in NAVCC collections.

The Library of Congress Recommended Formats Statement (RFS) lists DDP as an acceptable format for Audio - Media-independent (digital).

Limited.

Accessibility Features

As an authoring format, or protocol, DDP offers limited accessibility features. Subpicture data (such as subtitles or captions) may be defined by the DDPMS or test streams, and the protocol allows for inclusion of track files (track titles or descriptions). See MPEG-2 Encoding Family for information on DVD streams.