A Digital Cinema Package (DCP) is a collection of digital files used to store and convey digital cinema (DC) audio, image, and data streams.
The term was popularized by Digital Cinema Initiatives, LLC in its original recommendation for packaging DC contents. However, the industry tends to apply the term to the structure more formally known as the Composition. ("You PLAY a Composition, You do NOT play a Digital Cinema Package".) A DCP is a “packing crate” for Compositions, a hierarchical file structure that represents a title version. The DCP may carry a partial Composition (e.g. not a complete set of files), a single complete Composition, or multiple and complete Compositions.
The Composition consists of a Composition Playlist (in XML format) that defines the playback sequence of a set of Track Files. Track Files carry the essence, which is wrapped using Material eXchange Format (MXF). Two-track files at a minimum must be present in every Composition (see SMPTE ST429-2 D-Cinema Packaging - DCP Constraints, or Cinepedia): a track file carrying picture essence, and a track file carrying audio essence. The Composition, consisting of a Composition Playlist and associated track files, is distributed as a Digital Cinema Package (DCP). It must be underscored that a Composition is a complete representation of a title version, while the DCP need not carry a full Composition. However, as already noted, it is commonplace in the industry to discuss the title in terms of a DCP, as that is the deliverable to the cinema.
The Picture Track File essence is compressed using JPEG 2000 and the Audio Track File carries a 24-bit linear PCM uncompressed multichannel WAV file. Encryption may optionally be applied to the essence of a track file to protect it from unauthorized use. The encryption used is AES 128-bit in CBC mode.
In practice, there are two versions of Composition in use. The original and commonly used version is called Interop DCP. In 2009, a specification was published by SMPTE (SMPTE ST 429-2 Digital Cinema Packaging - DCP Constraints) for what is commonly referred to as SMPTE DCP. SMPTE DCP is similar but not backward compatible with Interop DCP, resulting in an uphill effort to transition the industry from Interop DCP to SMPTE DCP. SMPTE DCP requires significant constraints to ensure success in the field, as shown by ISDCF. While legacy support for Interop DCP is necessary for commercial products, new productions are encouraged to distribute in SMPTE DCP.