How does a KDM work, and how can it go wrong?

Although some aspects of running a cinema have gotten simpler over the years, fixing some issues has come to require a higher level of technical know-how. The digital half of 'digital cinema' might seem daunting, but the principles that govern whether a piece of content is going to play back successfully are simple enough once you understand them. That's why we created our guide to troubleshooting KDM errors.

Click here to download it and learn all about how a KDM works, and what the most common causes of show-stopping errors are.

So what is a KDM?

A KDM (Key Delivery Message) is a small file generated by content mastering facilities (like Deluxe Technicolor Digital Cinema for example) and then sent to cinemas to unlock their content for playback. They have been around since 2006 in one form or another, and are currently in a format called 'SMPTE Modified Transitional 1'.


Why use KDMs?

Film studios go to great lengths to prevent the creation of unlicensed versions of their content and also want to ensure that cinemas are upholding their screening agreements. In light of the threat of digital piracy, when studios send digital content to cinemas, they encrypt it as a DCP (Digital Cinema Package) so that it could only be played exactly where they wanted it to be. KDM’s were created to decrypt these DCPs for playback of one specific piece of content at one screen over a pre-determined period of time. 

 

How does a KDM prevent unauthorised screenings?

Each screen in a digital cinema has a server connected to the projector that is required for playback. Each of these screen servers and projectors has their own unique identifiers, which are hard-coded into the KDM file when it is created. Content mastering facilities that produce KDMs refer to TDLs (Trusted Device Lists) that detail the identifiers for each individual piece of equipment, and use these to tell the KDM which screen server can unlock the content, and which projectors it is allowed to connect to.

 

What is a DCP?

A DCP consists of all the files that make up a digital film; the picture, sound, subtitles, and related information that will ensure the content is played out correctly. It may contain several different CPLs (Composition Playlist), which equate to different versions of the film. They are typically sent to cinemas on hard drives or via satellite, with each component of the DCP encrypted separately. 

 

What is a CPL?

CPLs are packaged into DCPs, and are instruction sets on how to build different versions of the same piece of content. For example, there would be a separate CPL for a feature with English or French subtitles. Instead of sending two full versions of the same film with the amended subtitles (which would take up twice the memory space), a DCP will consist of the feature, and two CPLs; one with the English subtitles, and one with the French. The instructions within each CPL would dictate how to insert the subtitles correctly into the feature.

 

What can go wrong?

These layers of security have been successful; there has never been a reported instance of content pirated during its journey from studio to cinema. However, they do make the system a little inflexible. If a cinema changes their schedule, they might have to request a new KDM with a different expiry date. If they unexpectedly need to replace a screen server that has stopped working, any KDMs they had for that screen will become invalid. If one of their auditoriums is out of service for maintenance, they cannot quickly transfer the showings to a different screen unless they already have valid KDMs for the rest of their complex. 

Nuances in the cause of these errors means that they can be difficult for staff on-site to trace, and result in longer troubleshooting times. Click on the link below to find out how to identify what could be causing your KDM errors, when to contact support, and print a troubleshooting checklist for quick diagnosis.


Troubleshoot your KDM errors

 


 

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