Cinema Distribution Requirements

Technical guideline for delivery to cinema

A Digital Cinema Package (DCP) is a data package intended for delivery to digital cinemas that contains all relevant AV data as well as metadata for screening. The structure within a DCP is specified by the Digital Cinema Initiative (DCI). For all individual elements contained within a DCP there are specifications about format and properties. The image information is stored in a DCP as a single frame sequence in JPEG2000 coding. 12-bit color depth and conversion to the XYZ color space are an essential part of the specification. The image material supplied for the JPEG2000 conversion must be progressive, i.e. available in full-screen format. The images can only have two aspect ratios in 2K or 4K.
A film can be shown with an aspect ratio of 1:1.85. This is called FLAT. In this case the image has a resolution of 1998x1080 px (2K), or 3996x2160 px (4K). Or the film is shown in an aspect ratio of 1:2.39. This is called SCOPE, the image has a resolution of 2048x858 px (2K), or 4096x1716 px (4K). Other formats or resolutions are not allowed.
If you want to deliver HD content (1920x1080) as DCP to a cinema, the image content must be embedded in a FLAT image (container). This results in narrow black stripes to the left and right of the HD image, called pillarboxes.
The frame rates are defined in the DCP standard as well. However, the specification to be used here must be observed. The "old" InterOP standard introduced in 2003 exists, which only allows 24 and 48fps in 2K and 24fps in 4K. The "new" SMPTE standard introduced in 2006 also allows 25, 30, 50 and 60fps (50 and 60fps only in 2K). With very diverse hardware standards in cinemas existing worldwide, it is possible that some old JPEG2000 cinema servers are still in operation that still only handle DCPs mastered according to the InterOP standard, although this has long been replaced by the SMPTE standard. If you want to transfer a TV movie to the cinema and avoid the conversion from 25 to 24fps, you should check in advance if an SMPTE-DCP with 25fps in the cinema of your choice is compatible.
The audio information can be stored in up to 16 discrete channels, i.e. individual mono WAV tracks. The sound is stored uncompressed in 24 bit sampling depth and with 48 or 96 kHz sampling rate. A DCP may contain several language versions. Accordingly, the corresponding audio tracks for the respective language versions must be available in the DCP. Both the image and the audio information is packed as MXF and stored in the DCP. The DCP also contains subtitles. It is possible to store several subtitle versions within one DCP. The subtitles are organized in XML files, which in turn must be formatted in the CineCanvas format.
A DCP with its different elements is organized by a CPL file, a "Composition Playlist".  This CPL contains information about which image, sound and subtitle versions can be played in which combinations. The structure and type of the name of a CPL is defined by the Digital Cinema Naming Convention. It is then possible to deduce the version, aspect ratio, etc. of a CPL. A schema according to which the correct and mandatory DCP-compliant name of your own film can be derived is found under undefined.
DCPs can also be encrypted to protect the content from unauthorized access. For this purpose a multi-level encryption procedure is used. The media files themselves are encrypted symmetrically with a 128bit AES key. However, the keys required for decryption are encrypted as well, this time asymmetrically with a 2048-bit AES key. The advantage of asymmetric encryption is that no key has to be transferred for decryption, but is already in the hands of the recipient. In this case it is the respective projector. This means that the DCPs are specifically encrypted for certain projectors and cannot be made visible in any other cinema except with the projector for which the DCP is intended. The information about which projector a DCP is intended for, the public key that blocks access to the DCP, and a pre-settable validity period for unblocking are located in the KDM, the Key Delivery Message, which is sent together as a mail.