A DCP is a collection of files used to store and convey digital cinema audio, image, and data streams.
The term “composition” is widely used in digital cinema. It was first used in the DCI specifications for the packaging of DC contents. It refers to the structure that includes the movie, audio, and subtitles. However, the industry tends to use the term to refer to the structure itself. A DCP is a packaging container for Composition, a file structure that represents a title version. It carries a partial Composition, a single complete Composition, or multiple and complete Composition.
A Composition contains a Composition Playlist 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 are required for 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 soundtrack, a Composition Playlist, and associated track files are distributed as a Digital Cinema Package (DCP). The Composition is a complete representation of one version of a movie, while the DCP need not carry a full Composition. However, it is commonplace in the industry to discuss the movie in terms of a DCP because that is the deliverable to the movie theater.
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.