Short answer
A DCP (Digital Cinema Package) is the digital package of a film prepared for cinema playback; it holds the picture, sound and subtitle files and is usually encrypted. A KDM (Key Delivery Message) is the digital key that unlocks that encrypted package on a specific hall's server within a specific date and time window. No DCP, no film; no valid KDM, no encrypted film.
DCP: the film's digital package
A DCP is built to the DCI specification and SMPTE standards. A typical package contains:
- Picture: JPEG 2000-compressed frames inside MXF files
- Sound: uncompressed multichannel PCM audio
- Subtitles: text- or image-based subtitle files
- Composition (CPL) and packing lists: XML files that define what plays in which order, plus validation data
Films reach cinemas on hard drives, by satellite or over the internet. After ingest, the package must be validated on the server as complete and uncorrupted; skip this and problems only show up during a show.
KDM: the key that opens the film
Most commercial releases arrive AES-encrypted. A KDM is an XML file carrying the decryption key, and it is tied to three things:
- A specific version of the film (CPL)
- A specific device: the certificate of the hall's media block (IMB); it will not work in another hall
- A specific time window: start and end date and time
Common screening problems
| Problem | Likely cause | Prevention |
|---|---|---|
| Film won't play, “no/invalid KDM” | KDM missing, expired or issued for the wrong device | Check KDM windows against the show schedule in advance |
| Film won't open on opening day | KDM start time is after the first show | Match the schedule with the KDM window |
| Error mid-show | Incomplete or corrupted DCP ingest | Validate after ingest (hash check) |
| Films stop opening after a projector/server change | KDMs issued for the old device certificate | Send the new certificate to distributors when equipment changes |
Organising content and KDM management
In multiplexes, tracking DCPs and KDMs by hand increases the risk of errors. A central content calendar, monitoring that warns before KDMs expire, and a TMS (Theatre Management System) that manages every hall from one screen reduce that risk.
Frequently asked questions
What does DCP stand for?
What does KDM stand for?
Can a KDM be used in another hall?
What should be done when a projector or server is replaced?
AHA DCS runs film delivery, ingest, validation and KDM tracking on your behalf.
Operations management