What is a Digital Cinema System and How do you get there (Part Two)?

In Part One we looked at what digital cinema is, and what a digital cinema system entails.

In this part we’ll go deeper into the DCI specification, and the steps involved to get there. Finally, we’ll tackle how you can best prepare your project for theatrical release.

Christie DLP Projector

Understanding DCI in detail

DCI (and most other digital cinema systems) tend to follow a ‘turnkey’ policy. This means they want to control every step of the process, and that includes the digital cinema system equipment (server, media, software and projector).

For this reason, any equipment connected to storing, transmitting and projecting DCI material must be ‘compliant’, according to the procedures laid out in the Compliance Testing Plan. Once the manufacturers of these equipments are sure their systems are compliant, DCI (or Testing Entities) will formally test it for the same. This is typical industry practice of any system, let alone cinema systems. To see what kind of test material is available, click here.

From these tests, those that pass are placed in the Compliant Equipment group, which I strongly urge you look at. There aren’t many players in this space. This allows DCI to keep a tight reign on quality control.

What makes a DCI server?

Dolby Server DSS200

A DCI server isn’t any different from any low-end computer server. All it needs to do is be reliable, stable and have fast sequential disk read access. If you open up a few servers, you’ll find:

  • Usually a low-end Supermicro motherboard with a Xeon processor and 8 GB RAM
  • A RAID 5 array enterprise-class hard drive (7,200 rpm), with an additional SATA expansion card if necessary. Usually you have four drives. It should be able to sustain 307 Mbps.
  • A hardware RAID card
  • Redundant power supply
  • Gigabit Ethernet Interface for connectivity
  • BNC interface card for HD-SDI
  • Software – Playback, Management and Security

That’s about it.You could put together such a system for about $1,500 or less. The projectors and lamps are expensive, as I’ve mentioned here. A typical 2-hour movie will come in under 500 GB, playing back at less than 75 MB/s, including audio (16-channel uncompressed audio is less than 20 Mbps, and a 2-hour movie will be less than 20 GB).

However, don’t let this fool you. It’s the software that makes a DCI server expensive. It has to run a right ship, without faults, with warnings, encryption, etc. It also plays back the media and manages the digital cinema system as a whole. It is really turnkey.

The server system is also called a Media Block, though according to DCI the Media Block primarily deals with the encryption and decoding part of the chain.

You don’t even need hardware RAID. You can use software RAID for playback. Additionally, you’ll need good quality speakers and a great screen.

How are all the parts connected? The most important connections on a server are the Ethernet (RJ45, which can be Copper and/or Fiber) and the dual HD-SDI BNC cables. Audio will typically use the RJ45 cables and video could use either. Modern servers will also have HDMI and LTC (Timecode) cables. They usually have the ability to playback DVDs and Blu-ray if required.

All said and done, you are basically playing back video at 250 Mbps (or 500 Mbps for HFR). As explained in Part One, Prores 4444 (12-bit, 2K) at 24 fps has a similar data rate, at 300 Mbps or so.

When you break it down like this, it isn’t complicated anymore, is it?

What are the four stages to a DCI experience?

Instead of progressing from start to finish, why not do it the other way around? Let’s start with DCI and work our way backwards.

The four stages to the DCI experience are:

  • DCI Playback (which is JPEG2000)
  • DCP (Digital Cinema Package)
  • DCDM (Digital Cinema Distribution Master)
  • DSM (Digital Source Master – Your master format)

Steps involved in DCI

You movie master (which they like to call the DSM) is the best representation of your work. Ideally, you’ll use a format that will become one of the DCDMs (I’ll explain this bit in the next section).

Once the DCDMs are created, it is packaged into the DCP. There can be many DCPs, depending on country, territory, whatever. In effect, DCPs are glorified containers, usually in the MXF format.

DCPs are transported to various movie theaters via shipped hard drives, internet or satellite.

The movie theater digital cinema system unwraps the package and plays back the file.

In many ways, these four stages are analogous as follows:

  • DCI – for the Exhibitor (Movie theater owner)
  • DCP – controlled by the Distributor
  • DCDM – controlled by the Producer/Post Facility
  • DSM – controlled by the Filmmaker

The question a filmmaker needs to ask is: Which parts of the process do I have control of?

You can’t do anything about the DCI playback system, since that’s fixed.

Similarly, you can’t do anything about the DCPs because its contents are determined by the distributor. Do you have a distribution deal in place already? If no, then there’s nothing you can do about the DCP. As mentioned earlier, DCI is only one of the many digital cinema systems in the world. If your movie is going to be seen in many countries, you might see many kinds of packages made, none of which are in your control. A DCP includes additional audio tracks, trailers, messages, logos, captions, subtitles, compression, encryption and security.

That leaves two choices – the DCDM and the DSM. Out of these two, DCI does not care what your DSM is: what color space it is in, what its resolution is, what format it is in, nothing. As explained in the Different Stages of Post Production, a Master can serve many purposes. What the DCI needs is a master that it understands, created according to its specifications.

It is the producer’s or filmmaker’s job to create the DCDM, either by themselves, or with the help of a post facility.

Preparing the DCDM

The DCDM is designed to be a format that can playback efficiently, while maintaining the best quality possible considering today’s technology. Here are the details:

  • 16-bit TIFF container holding 12-bit X’Y’Z’ material. The extra four bits are zeroes. Ideally, this should be uncompressed.
  • Directory will have TIFF files ordered in an image sequence (with leading zeroes). Different reels, different directories.
  • Directory name is in the format: NameofProject.Reel_# (where # is the reel number)
  • File (TIFF) name is in the format: NameofProject.Reel_#.xxxxxx.tiff (where xxxxx is the frame number)
  • Metadata that includes resolution, frame rate and frame count must be included in each TIFF file.
  • The audio container will be WAV (*.wav) and will always be uncompressed.
  • Subpictures, i.e., any imagery that will be overlaid over the TIFF file for projection, will be in PNG (which supports transparency). Subpictures are used for subtitles mostly. Subpicture ‘metadata’ is packaged as XML, which is a universal markup language.
  • Timed text (subtitles or captions) in text-form (as opposed to subpictures, which are in image form) are delivered as XML.
  • A minimum of six channels for audio (5.1), with support for 7.1, and a maximum of 16 channels.

Any type of content – your movie, logos (of organizations that have nothing to do with your movie but still appear at the beginning accompanied with loud music), advertisements, messages, trailers, etc. – are called Compositions in DCI language. Each composition is encoded in the exact same specifications.

A list of common compositions:

  • Image sequence
  • Audio
  • Pre-show content
  • Subpictures
  • Timed Text

Each composition is a DCDM, and the whole is also the DCDM. As a filmmaker, you’re only concerned about your movie. But your producer might add a few compositions of his own to the DCDM.

This means, your DCDM is a bunch of folders waiting on a hard drive. You can’t play it back properly because you don’t have the right audio sync, subtitle sync, and order of playback (a playlist), etc. All this is provided in the DCP process, which is basically making sense of it all. Again, you don’t decide the trailers, advertisements, etc. – that’s between the distributor and the exhibitor. Your job is provide as many DCDMs as is part of your agreement – your movie being the most important ‘composition’.

Just for your reference, the DCP wrapping ‘mechanism’ follows the MXF (Material Exchange Format) system, which you find in modern cameras. You don’t have to worry about that, though.

Note: What I’ve outlined is a general overview, with the explicit intention of helping a newcomer understand the process. For a full overview, read the entire DCI specification here. There are many more things I’ve barely even touched, like encryption, forensic marking and so on – let the distributors and exhibitors worry about it. Let them earn their bread, too.

How to ensure your movie is ready for theatrical release

Here’s the answer: Just make the best movie possible with what you have.

There is nothing you need to do specifically to ensure you comply with DCI – that’s one good thing about it. It’s not like a broadcast television specification. It’s much more lenient. Your movie – your terms.

If you can – only if you can – you could aim to do the following to deliver the best experience for your audience:

  • Get your movie graded in a DCI-P3 color space environment. Even though DCP is CIE X’Y’Z’, the projector will most likely be in DCI-P3, and it is good to know what it’ll look like in the end. This is not mandatory – there’s nothing special about DCI-P3.
  • Keep your master format (DSM) at equal to or greater than the distribution resolution. If you want your movie to be shown in a 4K movie theater, make your master 4K.
  • Keep your frame rate 24 fps, true 24 progressive frames per second if possible. Obviously, if your intention is a different playback frame rate, then stick to that.
  • Get the best audio you can, and mix it professionally in a theater environment. This is critical. This is actually a ‘must’, not an ‘if you can’.

What does this look like? Here are the specs:

  • 16-bit TIFF image sequence in whatever color space you want (could be ACES, Rec. 709, DCI-P3, whatever) and the best chroma sub-sampling you have (444, 422 or 420)
  • 24-bit 48/96 KHz uncompressed LPCM WAV, in at least a 5.1 mix
  • Decent captions and/or subtitles as PNG or XML

You can do this, can’t you? In fact, these specifications are great for any master, not just DCI. All the other sub-masters for various deliverables can be encoded from this master. It could be your archival format – the best representation of your work.

If you feel like creating your own DCP, try OpenDCP, an open-source DCP creator. For a full list of DCP creation ‘packages’, click here. As you can see, this is not worth wasting any time on, if you’re an indie filmmaker. For the sake of learning, though, check out this cool video that goes in-depth:

I hope this article has explained how you can ensure your movie is ready for theatrical distribution. Do you have any stories to share on how your movie made it to a movie theater?

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