What Is a DCP?
Updated
A DCP (Digital Cinema Package) is the set of files a cinema's server plays to show a film: the digital equivalent of a 35mm print, defined by the DCI specification (currently version 1.5.0) and SMPTE standards.
- • Picture: an MXF track file of JPEG 2000 frames in 12-bit X′Y′Z′ color, at up to 250 Mbit/s for both 2K and 4K.
- • Sound: an MXF track file of uncompressed 24-bit PCM, 48 or 96 kHz, up to 16 channels (5.1 and 7.1 are the usual layouts).
- • Playlists and checks: XML files. The CPL (Composition Playlist) sets what plays and in what order, the PKL (Packing List) lists every file with its hash, and the ASSETMAP says where each file is.
- • Frame rate: 24 fps as standard; DCI also allows 48 fps for 2K, and SMPTE DCPs can carry other rates.
- • Containers: 2K is 2048×1080, 4K is 4096×2160, with Flat (1.85:1) and Scope (2.39:1) framings inside them.
How Big Is a DCP?
A DCP's size is set by the picture bitrate the encoder uses, not by 2K or 4K. DCI caps picture at 1,302,083 bytes per frame at 24 fps, which is 250 Mbit/s. Size in GB = Mbit/s × seconds ÷ 8,000; the free bitrate calculator does it in your browser.
Worked example: a 2-hour feature (7,200 seconds)
- Picture at 250 Mbit/s: 250 × 7,200 ÷ 8,000 = 225 GB
- 5.1 sound, 48 kHz 24-bit: 6 × 48,000 × 24 = 6.9 Mbit/s → 6.2 GB
- XML (CPL, PKL, ASSETMAP): a few kilobytes
- Total: about 231 GB (about 119 GB if picture is encoded at 125 Mbit/s)
What's Inside a DCP
The picture, sound and package specs a cinema server expects
Picture
- JPEG 2000, at most 250 Mbit/s for both 2K and 4K (the DCI ceiling)
- 12 bits per component in X′Y′Z′, gamma 2.6 (SMPTE ST 428-1)
- Reference white 48 cd/m² (14 fL) on the cinema screen
- Flat (1.85:1) or Scope (2.39:1) inside a 2K or 4K container
Sound
- Uncompressed 24-bit PCM at 48 kHz (96 kHz is allowed)
- Up to 16 channels; 5.1 is the minimum a DCI system plays, 7.1 is optional
- 5.1 order: L, R, C, LFE, Ls, Rs on channels 1–6; channels 7 and 8 carry HI and VI-N
- Dolby Atmos or SMPTE IAB immersive sound travels as a separate auxiliary track file
Package
- CPL (Composition Playlist): what plays, reel by reel
- PKL (Packing List): every file with its size and SHA-1 hash
- ASSETMAP: where each file is (ASSETMAP.xml in a SMPTE DCP)
- Optional AES-128 encryption, unlocked by a KDM
2K and 4K: Containers, Framing and Frame Rates
The picture sits inside a fixed container. A Flat film fills the container's height, a Scope film its width; the rest is not stored. The bitrate ceiling is the same at 2K and 4K, so a 4K DCP is no bigger than a 2K one at the same bitrate. The free aspect ratio calculator finds the largest frame of any ratio inside a container, and the aspect ratio cheat sheet lists the Flat and Scope sizes. Shooting anamorphic for Scope? The anamorphic desqueeze guide shows which squeeze and sensor area land on 2.39:1, and the free anamorphic calculator checks yours.
2K DCP
- Container:
- 2048×1080 container
- Bitrate:
- Up to 250 Mbit/s
- Picture size:
- Up to 112.5 GB per hour
- Frame rates:
- 24 or 48 fps (DCI); 25, 30, 50, 60, 96, 100, 120 fps (SMPTE ST 428-11)
4K DCP
- Container:
- 4096×2160 container
- Bitrate:
- Up to 250 Mbit/s
- Picture size:
- Up to 112.5 GB per hour
- Frame rates:
- 24 fps (DCI); 25 or 30 fps (SMPTE ST 428-11)
SMPTE vs Interop DCP
There are two ways to package a DCP. Interop came first and is still played everywhere; SMPTE is the standardized version the industry has been moving to since the early 2010s. Make SMPTE DCPs unless a venue asks for Interop.
| SMPTE DCP | Interop DCP | |
|---|---|---|
| Status | The current standard (SMPTE ST 429-2; the SMPTE RDD 52 profile sets out how to build one) | Legacy format; servers must still play it |
| Subtitles | SMPTE ST 428-7 timed text wrapped in an MXF track file, which can be encrypted | A loose XML file that cannot be encrypted and needs its own folder layout |
| Sound channels | Channels can be labeled, so a server can tell 5.1 from 7.1 | One fixed channel mapping, no labels |
| Asset map file name | ASSETMAP.xml | ASSETMAP |
Encryption and KDMs
An encrypted DCP is useless without its key. Keys travel separately in a KDM (Key Delivery Message, SMPTE ST 430-1), an XML file made for one server's security certificate and valid only between two dates. Ask each venue for its server certificate well before the screening.
Encrypted DCP
Plays only with a KDM
- Picture, sound and subtitles are encrypted with AES-128
- Each KDM is made for one server's certificate and a set play period
- A KDM that has expired, or was made for another server, will not open the content
- The norm for commercial releases
Unencrypted DCP
Plays on any compliant server
- No keys to issue, track or reissue
- Common for festivals, test screenings and trailers
- Anyone with the drive can copy and play it
- Simpler to troubleshoot on site
Subtitles and Captions
- • Format: a SMPTE DCP carries subtitles as SMPTE ST 428-7 timed text, an XML document wrapped in its own MXF track file. Text needs an OpenType font, which travels with the subtitles; image subtitles use PNG files.
- • Open or closed: open subtitles and captions appear on the main screen for everyone. Closed captions go to a personal display device for viewers who are deaf or hard of hearing, and should include sound descriptions.
- • Burned in: subtitles can also be rendered into the picture. That always works, but can't be switched off and needs a separate picture encode for each language.
Making a DCP, Step by Step
Prepare the Master
Finish picture and sound at the specs the DCP will carry.
A 2-hour ProRes 4444 XQ master at 24 fps is about 1.5 TB at 4096×2160 (1,697 Mbit/s) and about 408 GB at 2048×1080 (453 Mbit/s)
Encode
Turn picture and sound into JPEG 2000 and PCM track files.
Picture per hour = bitrate × 0.45: 250 Mbit/s (the DCI ceiling) = 112.5 GB; 125 Mbit/s = about 56 GB
Package
Write the playlists and checksums that let a server ingest the DCP.
Package overhead: the CPL, PKL and ASSETMAP are XML files of a few kilobytes each
Check
Verify the package before it leaves the building.
Every asset in the PKL carries a SHA-1 hash, so a corrupted copy shows up at ingest
Storing and Delivering a DCP
Size per hour
- • Picture (2K or 4K): up to 112.5 GB at the 250 Mbit/s ceiling; about 56 GB at 125 Mbit/s
- • Sound, 5.1 at 48 kHz/24-bit PCM: about 3.1 GB (16 channels: about 8.3 GB)
- • Subtitles: the XML is small; any embedded font adds its own size
- • Package files: a few kilobytes of XML
Delivery
- • Drives: ISDCF recommends an MBR drive with a single Linux partition formatted ext2 or ext3 (128-byte inodes) for the widest compatibility. MBR limits these drives to 2 TB
- • Upload: a 231 GB feature takes about 31 minutes at a sustained 1 Gbit/s and about 5 hours at 100 Mbit/s (the free upload time calculator works it out for your line); see storage planning for working space
- • Name the package with the ISDCF naming convention so projectionists can tell versions apart
- • Keep a verified copy of the DCP and of the master it was made from
Common DCP Problems
- • Color shifts from a wrong conversion to X′Y′Z′, typically a Rec. 709 master treated as P3 or the other way round
- • Surrounds or LFE coming out of the wrong speakers because the channels are out of order
- • Sound drifting out of sync when a 23.976 master is not conformed to 24 fps; the audio sample rates guide covers the 0.1% pull-up
- • A Scope film letterboxed inside a Flat container, or the reverse, so it plays small on screen
- • KDMs made for the wrong server certificate, or for dates that don't cover the screening
- • Drives formatted in a file system the cinema server can't read
- • Subtitles that are missing because the font was not included
DCP Questions
What does DCP mean?
DCP stands for Digital Cinema Package: the set of files a cinema's playback server reads to show a film. It is the digital replacement for a 35mm print.
What is the DCP file format?
A DCP is a folder, not a single file. Picture and sound are MXF track files: picture is JPEG 2000 in 12-bit X′Y′Z′ color, sound is uncompressed 24-bit PCM at 48 or 96 kHz with up to 16 channels. XML files tie them together: the CPL (Composition Playlist) says what plays in what order, the PKL (Packing List) lists every file with its hash, and the ASSETMAP says where each file is.
How big is a DCP?
Size follows the picture bitrate. DCI caps picture at 250 Mbit/s for both 2K and 4K, so a 2-hour feature at the ceiling is 250 × 7,200 ÷ 8,000 = 225 GB of picture plus about 6 GB of 5.1 sound, roughly 231 GB. Encoded at 125 Mbit/s the same film is about 119 GB.
What resolutions and frame rates does a DCP use?
2K DCPs use a 2048×1080 container (Flat 1998×1080, Scope 2048×858); 4K uses 4096×2160 (Flat 3996×2160, Scope 4096×1716). The DCI specification requires 24 fps and allows 48 fps for 2K. SMPTE ST 428-11 adds 25 and 30 fps at 2K and 4K, and 50, 60, 96, 100 and 120 fps at 2K only. Check that the venue can play anything other than 24 fps.
Should I make a SMPTE or an Interop DCP?
SMPTE, unless a venue asks for Interop. SMPTE DCP is the standardized format (SMPTE ST 429-2) and supports encrypted subtitles and labeled audio channels. Interop is the older format the industry has been moving away from since the early 2010s, although servers still play it.
What is the difference between an encrypted and an unencrypted DCP?
An encrypted DCP only plays with a KDM (Key Delivery Message) made for a specific server's certificate and a set play period, which is how commercial releases are protected. An unencrypted DCP plays on any compliant server, which is common for festivals and test screenings.