The emergence of digital cinema has rapidly changed the way a movie is presented to an audience. The major studios pushed the conversion of theaters to digital. The Digital Cinema Initiatives (DCI) was created by six major studios and published a system specification for digital cinema. It provided a set of global standards for equipment manufacturers and movie makers to follow to insure the movies could be shown in all locations.
The specification establishes that picture encoding is done using the ISO/IEC 15444-1 "JPEG2000" (.j2c) standard. It also requires the use of the CIE XYZ color space. Two levels of resolution are supported: 2K (2048×1080) at 24 or 48 frames per second, and 4K (4096×2160) at 24 frames per second. The sound component provides for up to 16 channels of uncompressed audio using the "Broadcast Wave" (.wav) format at 24 bits and 48 kHz or 96 kHz sampling.
This change in how movies are exhibited has created a need for independent film makers to deliver their movies in the required digital format. This digital format comes in a set of files delivered in a Digital Cinema Package (DCP). The file structure of a DCP is organized into a number of Material eXchange Format (MXF) files that store audio and video streams, and auxiliary index files in XML format that tell the digital server how to display the movie.
Any movie that is to be presented using a digital projection system must be converted to a Digital Cinema Package. The DCP conversion process consists of rendering the images to JPEG2000 images with a change in color space to CIE XYZ color space. The audio files are also converted to the required format. These files and the additional control files are stored in a folder:
- Picture MXF files - Picture contents may be stored in one or more reels corresponding to one or more MXF files. Each reel contains pictures in JPEG 2000 format.
- Sound MXF files - Sound contents are stored in reels, too, corresponding to picture reels in number and duration. Each file contains linear PCM essence.
- Asset map file - List of all files included in the DCP, in XML format.
- Composition playlist file - Defines the playback order of each picture and sound reel during presentation and is saved in XML format.
- Packing list file - All files in the composition are hashed and their hash is stored here, in XML format.
- Volume index file - The xml file VOLINDEX is used to identify the volume order in the series.
The files are delivered on disk drives to the theater. Trailer DCPs are small enough to be delivered on a USB thumb drive or downloaded via a high speed internet connection. Feature DCPs are delivered on a portable hard drive or on the industry standard CRU DX115 disk drive. The hard drives are usually formatted in the Linux EXT2 or EXT3. NTFS and FAT32 are also occasionally used. Large distribution movies are delivered on the CRU DX115 since it can be inserted in the external drive bays on most servers which allows for faster transfer to the servers disk drive systems. Portable hard drives connect via USB connections that are typically at USB 2.0 speeds. For smaller files like trailers, this is insignificant. For larger feature files, additional time is needed to ingest the movie into the cinema server.
More Information on Digital Cinema Packages