Digital Cinema Quietly Reaches Major Milestone With SMPTE DCP
by Michael Karagosian
©2009 MKPE Consulting LLC All rights reserved worldwide
originally published in the 30 March 2009 issue of Digital Cinema Report
A major milestone was quietly reached in March with the publication of the last in the suite of D-Cinema Packaging (DCP) standards by the Society of Motion Picture and Television Engineers, also known as SMPTE. This is an effort that has taken over seven years to fulfill. Publication of the full suite of packaging standards paves the way for studios to distribute fully compliant SMPTE distributions, eliminating the need for major equipment upgrades. Full implementation of the standards in digital cinema equipment could take place as early as 2010.
"Packaging" is the term used to describe the method by which digital files are prepared for distribution and playout from digital cinema equipment. The concept for standardized packaging in digital cinema dates back to late 2001. At that time, I called a meeting with a small group of top experts in the field, all of whom were keen to develop a standard distribution package. In cinema, the workflow requirements are different from those for DVD and the broadcast industry. Digital cinema demands a method of organizing files that at that time had never before been developed.
In part, this is because digital cinema is a replacement technology for film. In technical parlance, it is called a "store-and-forward" technology, versus "streaming" technology. To give an example from the web, store-and-forward is when you purchase a copy of a movie from a web site, and download it onto your hard drive. Once downloaded, you click on it to play it any time you want, whether you're connected to the network or not. Streaming is when you click on a website link to play a movie, and a copy is not stored on your hard drive. The file remains on the web server, and you can only view it as long as your network connection is good, allowing the movie to "stream" to your computer.
Other differences also exist. The use of reels, which are temporal chunks of content, are the norm for film-based movie distributions. If last minute changes are made by the distributor, the changes are generally limited to a reel. Only the changed reel is sent to the exhibition site. Such functionality is not present, nor is it needed, in the way DVDs are made, or in streamed broadcasts. But with digital store-and-forward, this simple functionality is very desirable, leading to efficient content distribution. For this reason, digital cinema packaging embraces the concept of a digital "reel." A digital reel is simply a set of files that make up a temporal chunk of the movie.
While there were features of film that were well liked which we needed to embrace, there were also features we wanted to improve on. The most prominent of these is the marriage of audio and image. The industry needed a way to distribute multiple languages to a site, for instance, without being forced to distribute the picture multiple times.
It was natural to conclude that the digital cinema package had to include a separate digital file for every type of content, or essence type. For example, picture is on a separate file from audio. A playlist was needed to instruct how to play all of these files. This couldn't be a playlist, however, that was editable by users without detection. Months later, as we dove into details, the decision was made to use a technique called Material Exchange Format, or MXF, to wrap the files, so that metadata, or "data about the data," could be stored along with the essence. MXF itself was so new that the digital cinema packaging group was providing input to the MXF group within SMPTE to shape the technique as MXF standards emerged. But we broke away from the MXF camp in deciding to use a different technology called Extensible Markup Language, or XML, for the playlist.
The experts that joined me that first meeting in 2001 were Mike Bruns, Dave Dawson, John Hurst, Jean-Francois Nivart, and. Kevin Wines. Nearly all of the concepts that came out of our first meeting survived the scrutiny of our peers, and became the foundation of the body of work that we now call D-Cinema Packaging, or DCP. Of that initial group of six, four of us remain involved in digital cinema today. One member, John Hurst, built a business providing software for encrypting and packaging content, and remains a major contributor and architect of the overall SMPTE packaging effort.
Over the years, many details needed to be addressed, and many contributors stepped up to contribute and debate various techniques to ensure that this work was robust. DCI codified the early SMPTE packaging concepts in its specification, but even that work now only describes a subset of the complete SMPTE D-Cinema Package. Additional capabilities were needed, and in the past year the work for labeling audio formats and packaged closed captions was finalized. Had anyone suggested back in 2001 that it would take a little over 7 years to finish this work, no one would have believed it.
So is this it, can we go home now? Well, I have this other little piece called NATO's Digital Cinema Requirements that, in part, sets the stage for making equipment interoperable within the cinema environment. Of course, this will only take a little while to complete...