Every Composition is defined by a Composition Playlist, or CPL. As the name suggests, the CPL defines and orchestrates the playback of all Track Files that comprise the Composition. It does so temporally, in a reel-by-reel fashion. Each version of a title will have a unique CPL This could be a version having a certain picture type (a particular aspect ratio, or 2D vs 3D), a different sound mix (say, 5.1 or 7.1), a sound track in a particular language, subtitles in a particular language, and so on.
While title versions require a unique CPL, the Track Files associated with each CPL do not have to be unique. A set of Picture Track Files, for example, can be shared by many CPLs, each CPL defining a different version of the work based on the same Picture Track File, but having other Track Files of different essence types that are unique to that version.
The CPL is an XML data file whose metadata defines the Composition that it represents. A description of the CPL’s data elements is presented below:
|Composition Playlist (CPL) Element||Description|
|CPL Identifier||Identifies this instance of the Composition, encoded as a Universally Unique IDentifier (UUID) per RFC 4122|
|Content Version Identifier||Identifies the version of content of which this Composition is an instance, encoded as a Universally Unique IDentifier (UUID)|
|Reel List||A list by Reel of the Track File assets to be reproduced, in the order they are to be played|
|Content Title Text||Title of the work|
|Annotation Text||Text field, typically defined by the Digital Cinema Naming Convention|
|Content Kind||An attribute naming the type of content in the Composition per SMPTE 429-7|
|Rating||An agency rating of this work. In the US, this would be an MPAA rating|
|Issue Date||Time and date when the CPL was issued|
|Issuer||Optional text field naming the issuer|
|Creator||Optional text field identifying the application used to create the Composition|
|Signer||If digitally signed, this carries the public key of the entity that signed the CPL|
|Digital Signature||Optional, used to authenticate the CPL|
For a complete description of the SMPTE CPL, please refer to SMPTE S429-7 Composition Playlist. The top-level document that defines the DCP and Composition is SMPTE ST 429-2 DCP Operational Constraints.
The CPL carries metadata that describes the Composition, but in practice, more data is needed to benefit cinema operators. An ad-hoc nomenclature is often used for this purpose called the Digital Cinema Naming Convention. The Naming Convention prescribes a human-readable text field carried by the CPL Annotation Text element. It was devised as a stop-gap measure until a means to include additional metadata in the Composition was devised. A standard that accomplishes this is now available, titled ST 429-16 Additional Composition Metadata and Guidelines.