The Digital Cinema Distribution Master (DCDM).

A Digital Cinema Initiative Distribution Master (DCDM) is a collection of all the necessary DCP (Digital Cinema Package) components for conveying images, sound, subtitles, metadata and other language versions for a digital cinema presentation.

These components must comply with the Digital Cinema Initiative (DCI ) specifications.

The image must be mastered for only two types of container:
FLAT 1:1.85 (2K: 1998x1080; 4K: 3996x2160)
CINEMASCOPE 1:2.39 (2K: 2048x858; 4K: 4096x1716).

The DCDM image structure is stored as a 12-bit TIFF file which is placed into the most significant bits of a 16-bit word, with the remaining 4-bits filled with zeros.

The sound is stored as a 24-bit uncompressed Broadcast WAV file in 5.1 and sampled at 48 or 96kHz.

The DCDM must have been generated from the DSM (Digital Source Master). It is not permissible to derive the DCDM from the DCP . The DSM is the source data from the final colour correction and final audio master mix of a film. So a DSM serves as the basis for the compilation of DCDMs, which in turn combine all the elements that are needed for a Digital Cinema presentation (or generating a DCP for the same purpose).

There are two further uses for the DCDM. Firstly, it serves as an uncompressed master for archival purposes and secondly, it can serve as a direct source for a demonstration of the material. Then it is referred to as DCDM and sent directly to a projector from the media block. In this case, the media block must of course be able to playback the DCDM in real-time.

Where the aspect ratio of the DSM is for any reason a non DCI-compliant container, such as HD video 1:1.78, the image must be scaled to fit at least one corresponding dimension in the FLAT-container (1:1.85). So an HD video 1:1.78 aspect ratio image would fill the vertical height but would require vertical black edges added to the left and right of the picture to fit into the 1:1.85 aspect ratio width. This is known as ‘pillarboxing’.

DCDMs are important for archiving of feature films. By compressing, and often simply just by encrypting a DCP it is not suitable as a master source material for additional versions of the film or even the creation of further DCPs. A DCP can be regarded as purely a screening copy that is created just for this purpose. If one wants to permanently archive a cinematic work at the highest quality and accessibility then all the relevant DCDMs must be used.

Each country may well have specifications for archiving film as specified by their national film institutes. For example, they may ask for compliance with the current version of the SMPTE standard ST:428 that covers DCDMs. The British Film Institute (BFI) in the UK provides a ‘Collection Policy’ for material it archives. In that it states:

“Digital Cinema: Digital masters in DPX format or Distribution Masters (DCDM) to SMPTE standards (images stored as linear TIFF in x,y,z colour, with 48kHz WAV audio). Digital Cinema Packages (DCP) are not preferred (they are highly compressed) but if we do accept a DCP it must be unencrypted.”