DCP explained

If you want to display your film in a digital cinema at highest possible quality, equivalent to a 35mm film print, DCP is the way to go. DCP (Digital Cinema Package) is a world wide standard ‘file format’, playable in every digital cinema all over the world.

Since colorists are one of the last persons handling the material before it is distributed it might be good to know what DCP is and what you need to deliver.

A DCP is not just a file format like quicktime. A DCP is a set of files and all these files are required by the digital cinema play-out systems. The DCP contains a very high resolution copy of the images and audio.

DCP uses XYZ color space and JPEG2000 codestream for the images.

CIExy1931

The XYZ color space is a large gamut color space and was designed to be able to describe all colors visible to humans and how the three types of color sensing cells in the retina perceives color.

JPEG 2000 is a new image coding system that uses state-of-the-art compression techniques based on wavelet technology. With this coding technology, images could be compressed harder without noticeable artifacts, like blocking.

the DCP package

There are 2 ways to create the DCP package, Interop and SMTPE. Interop is the older one and is supported by all digital projection systems, but SMPTE has support for more frame rates and MXF wrapped subtitles.

Interop supports

  • 24 and 48 fps @ 2K (MXF Interop can be encoded at 25 frame/s but support is not guaranteed)
  • 24 fps @ 4K
  • 24 fps @ 2K stereoscopic
  • 23.976 and 24 fps @ 1920×1080 (MPEG2)

SMTPE supports

  • 24, 25, 30, 48, 50, and 60 fps @ 2K
  • 24, 25, and 30 fps @ 4K
  • 24 and 48 fps @ 2K stereoscopic

The sizes supported are

  • Flat (1998×1080 or 3996×2160)
  • Scope (2048×858 or 4096×1716)
  • HDTV (1920×1080 or 3840×2160)
  • Full (2048×1080 or 4096×2160)

After colorspace conversion and compression, the JPEG2000 image sequence is wrapped into a Material eXchange Format, an MXF file.

Audio is loss-less (24 bit 48 or 96 kHz) and can handle up to 12 independent channels. The audio files are also wrapped into an MXF file.

Subtitles are stored in XML-files (Interop) or MXF-files (SMTPE).

One of the great features of a DCP is that it can contain multiple compositions (Component playlist). i.e. Different video version, language adaptions and subtitle tracks. This means that you can create one DCP package which works all over the world.

directory-list

  • each folder contains a subtitle track.
  • the ASSETMAP contains a list of files included in the DCP package with their relative paths.
  • the AUDIO.mxf contains the audio tracks.
  • the cpl XML files are Component playlists, they contain the DCP title and describe the Video, Audio and Subtitle track.
  • the pkl XML file is a Packaging list, it describes the assets, file sizes, hash and type.
  • the VIDEO.mxf contains the video.
  • the VOLINDEX file describes if the DCP package is on more then one disk. Today most disks are so big that this is hardly used anymore.

The DCP package can also be AES encrypted. The encryption keys are generated and transmitted via a KDM (Key Delivery Message) to the projection site. KDMs are XML files that can be opened 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.

Thanks to Christer Engström for helping me with this article.

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