What is a Digital Cinema Package?
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 has been defined by Digital Cinema Initiatives, LLC in their recommendations for packaging of DC contents. General practice adopts a file structure that is organized into a number of usually multi-gigabyte size MXF files, which are separately used to store audio and video streams, and auxiliary index files in XML format.
The MXF track files contain image and audio essence that are compressed and encoded in order to reduce the huge amount of required storage. Encryption is an optional solution and is used to protect from unauthorized use. The image track file contains compressed JPEG 2000 essence and the audio is a wrapped 24bit linear PCM multichannel WAV file. The adopted (optional) encryption standard is AES 128 bit in CBC mode.
The newer SMPTE standards are used to conform the recommendations among different tool vendors and producers. Interop, the legacy DCP standard, is still required to be supported by DCP players.
What steps are involved in the DCP creation?
Most film producers and distributors rely on digital cinema encoding facilities to produce and quality control check a digital cinema package before release. Facilities follow strict guidelines set out in the DCI recommendations to ensure compatibility with all digital cinema equipment. For bigger studio release films, the facility will usually create a DCDM (Digital Cinema Distribution Master).
A DCDM is the post-production step prior to a DCP. The frames are in XYZ TIFF format and both sound and picture are not yet wrapped into MXF files. A DCP can be encoded directly from a DCDM. A DCDM is useful for archiving purposes and also facilities can share them for international re-versioning purposes. They can easily be turned into alternative version DCPs for foreign territories. For smaller release films, the facility will usually skip the creation of a DCDM and instead encode directly from the DSM (Digital Source Master) the original film supplied to the encoding facility. A DSM can be supplied in a multitude of formats and colour spaces. For this reason, the encoding facility needs to have extensive knowledge in colour space handling including, on occasion, the use of 3D LUTS to carefully match the look of the finished DCP to a celluloid film print. This can be a highly involved process in which the DCP and the film print are “butterflied” (shown side by side) in a highly calibrated cinema.
Less demanding DCPs are encoded from tape formats such as HDCAM SR. Quality control checks are always performed in calibrated cinemas and carefully checked for errors. QC checks are often attended by colourists, directors, sound mixers and other personnel to check for correct picture and sound reproduction in the finished DCP.
Can the DCP be encrypted?
The distributor can choose to encrypt the media (MXF) files with AES encryption to combat piracy. The key pairs used for encryption are different for every projector, so the decryption keys are generated and transmitted via a KDM (Key Delivery Message) separately to the projection site. KDMs are XML files containing decryption keys that can be used only by the destination device. A KDM is associated to each playlist and defines the start and stop times of validity for the projection of that particular feature.
What DCP delivery methods are used?
The most common method uses a specialist hard disk (most commonly the CRU DX115) designed specifically for digital cinema servers to ingest from. These hard drives were originally designed for military use but have since been adopted by digital cinema for their hard wearing and reliable characteristics. The hard drives are usually formatted in the Linux EXT2 or EXT3 format as D-Cinema servers are typically Linux based and are required to have read support for these file systems. Usually the iNode is set to 128 bits to avoid compatibility issues with some servers. Also, NTFS and FAT32 are occasionally used. Hard drive units are normally hired from a digital cinema encoding company, sometimes in quantities of thousands. Drives are commonly shipped in protective hard cases. The drives are delivered via express courier to the exhibition site. Other, less common methods adopt a full digital delivery, using either dedicated satellite links or high speed Internet connections.