Frequently asked questions

Wolfgang Woehl edited this page Nov 27, 2013 · 34 revisions

Digital Cinema Specification Documents

Where can I get the SMPTE D-Cinema specification documents?

Standards documents are sold by SMPTE. Required reading if you want to do anything beyond using available authoring apps.

Where can I get the Interop DCP specification documents?

Read SMPTE and Interop DCP Guidelines Including Accessibility (PDF). This document is maintained by MKPE Consulting LLC (who host numerous interesting resources). Section Transitional 1, or JPEG Interop or Interop DCP (Legacy Format) lists the required set of Interop documents which are available at ftp://ftp.digicine.com/Document_Release_2.0. In order to receive access credentials you will need to contact the current gatekeeper (mkpe.com) who will forward your request to the ftp.digicine.com maintainers.

In other words: Interop DCP is a de-facto standard everyone is using but is not actually published.

Which are the relevant SMPTE D-Cinema documents?

Production:

  • ST 428-1-2006 D-Cinema Distribution Master — Image Characteristics
  • ST 428-2-2006 D-Cinema Distribution Master — Audio Characteristics
  • ST 428-11-2009 Additional Frame Rates for D-Cinema
  • ST 428-21-2011 Archive Frame Rates for D-Cinema

Post Production:

  • ST 428-1-2006 D-Cinema Distribution Master — Image Characteristics
  • ST 428-2-2006 D-Cinema Distribution Master — Audio Characteristics
  • ST 428-3-2006 D-Cinema Distribution Master — Audio Channel Mapping and Channel Labeling
  • RP 428-4-2010 D-Cinema Distribution Master — Audio File Format and Delivery Constraints
  • RP 428-5-2010 D-Cinema Distribution Master — Mapping of Images into Constrained Tag Image File
  • ST 428-7-2010 D-Cinema Distribution Master — Subtitle
  • ST 428-10-2008 D-Cinema Distribution Master — Closed Caption and Closed Subtitle
  • EG 432-2-2006 Digital Source Processing — D-Cinema Low Frequency Effects (LFE) Channel Audio Characteristics

Distribution Package (DCP):

  • ST 429-2-2009 D-Cinema Packaging — DCP Operational Constraints
  • ST 429-13-2009 D-Cinema Packaging — DCP Operational Constraints for Additional Frame Rates
  • ST 429-3-2007 D-Cinema Packaging — Sound and Picture Track File
  • ST 429-10-2008 D-Cinema Packaging — Stereoscopic Picture Track File
  • ST 429-5-2009 D-Cinema Packaging — Timed Text Track File
  • ST 429-12-2008 D-Cinema Packaging — Caption and Closed Subtitle
  • ST 429-4-2006 D-Cinema Packaging — MXF JPEG 2000 Application
  • ST 429-6-2006 D-Cinema Packaging — MXF Track File Essence Encryption
  • ST 429-7-2006 D-Cinema Packaging — Composition Playlist
  • ST 429-8-2007 D-Cinema Packaging — Packing List
  • ST 429-9-2007 D-Cinema Packaging — Asset Mapping and File Segmentation

Security:

  • ST 430-2-2006 D-Cinema Operations — Digital Certificate
  • ST 430-3-2008 D-Cinema Operations — Generic Extra-Theater Message Format
  • ST 430-1-2006 D-Cinema Operations — Key Delivery Message
  • ST 430-4-2008 D-Cinema Operations — Log Record Format Specification
  • ST 430-5-2008 D-Cinema Operations — Security Log Event Class and Constraints
  • ST 430-6-2010 D-Cinema Operations — Auditorium Security Messages for Intra-Theater Communications
  • ST 430-7-2008 D-Cinema Operations — Facility List Message

Projection:

  • ST 431-1-2006 D-Cinema Quality — Screen Luminance Level, Chromaticity and Uniformity
  • RP 431-2-2007 D-Cinema Quality — Reference Projector and Environment
  • RP 428-6-2009 D-Cinema Distribution Master — Digital Leader

Exhibition:

  • ST 430-6-2010 D-Cinema Operations — Auditorium Security Messages for Intra-Theater Communications
  • ST 430-10-2010 D-Cinema Operations — Auxiliary Content Synchronization Protocol
  • ST 430-11-2010 D-Cinema Operations — Auxiliary Resource Presentation List

Reference:

  • ST 431-1-2006 D-Cinema Quality — Screen Luminance Level, Chromaticity and Uniformity
  • RP 431-2-2007 D-Cinema Quality — Reference Projector and Environment
  • EG 432-1-2010 Digital Source Processing — Color Processing for D-Cinema
  • ST 428-1-2006 D-Cinema Distribution Master — Image Characteristics
  • ST 428-2-2006 D-Cinema Distribution Master — Audio Characteristics
  • ST 433-2008 D-Cinema — XML Data Types
  • ST 428-9-2008 D-Cinema Distribution Master — Image Pixel Structure Level 3 – Serial Digital Interface Signal Formatting
  • ST 428-19-2010 D-Cinema Distribution Master — Additional Frame Rates Level AFR2 and Level AFR4 – Serial Digital Interface Signal Formatting
  • RDD 20-2010 Cinelink 2 Specification
  • RP 428-6-2009 D-Cinema Distribution Master — Digital Leader

Where can I get the CineCanvas specification document?

See Texas Instruments’ DLP Cinema Technical Documents for The CineCanvas Specification – Rev C (pdf). This document describes the XML file format used by the DLP Cinema Subtitling Process which in turn is used in Interop DCP.

FAQ Contents

DCP, AssetMap, PackingList, CompositionPlaylist

What is a DCP? What is a Digital Cinema Package?

A Digital Cinema Package (DCP) is a collection of assets, listed in a PackingList document, supported by an AssetMap document.

Consider how this definition does not explicitly mention CPL or Composition or Audio trackfile. The reason is: A DCP does not have to carry a CPL, it does not have to carry image or audio essence either. It can, of course, and in most cases it will.

What is a composition? What is a CPL? What is a CompositionPlaylist

In Digital Cinema a composition (or CompositionPlaylist) is a timeline consisting of at least one Reel which in turn references the required assets for content playback. Usually a Reel will reference MainPicture and MainSound elements, at least. There can be elements for subtitles, closed captions and markers as well.

Another way to think of it: A composition defines precisely what will be seen and heard in the theatre. Much like the timeline of an editing application would define what’s to be seen and heard on the monitor in master playout.

Compositions can define non-zero entry points for assets, for example in order to skip leader footage etc.

What is an asset?

Anything a Digital Cinema composition will reference for playback is an asset: Pictures, audio, timed text. In addition PackingList documents, which list the content of a Digital Cinema Package, are assets as well. In Digital Cinema context an asset is identified exclusively by a unique number.

What is an Assetmap?

An AssetMap maps files to numbers. Numbers are used extensively in digital cinema packages to identify things. Everything (picture, video and audio files, subtitle files, compositions etc.) has a unique number. Here’s a snippet from an actual AssetMap:

<Asset>
  <Id>urn:uuid:483c3e49-837d-42af-bf9b-887282966963</Id>
  <ChunkList>
    <Chunk>
      <Path>some_mxf_file.mxf</Path>
    </Chunk>
  </ChunkList>
</Asset>

This snippet says The asset with the number 483c3e49-837d-42af-bf9b-887282966963 is found at the file location some_mxf_file.mxf

When ingesting a digital cinema package these number/file pairs will be added to an internal dictionary which keeps track of all the numbers and files. How a server does that varies. But the mechanism will reproduce the essential property of the AssetMap: Numbers pointing at files.

Every time a playback system needs something for playback it will search the internal dictionary for the required number. The dictionary will know where to find the asset with that number.

Our Interop DCPs are working just fine. Why should we switch to SMPTE DCP again?

2013 here. If you are still generating Interop DCP today, thinking I’m not going to fix what ain’t broken: Please consider transforming your workflow towards SMPTE DCP. If only for the benefit of selling a future-proof product to your clients. Use Interop DCP as a fall-back, a last resort to target legacy systems (which will go away in the foreseeable future).

Here are your and your clients’ benefits for using SMPTE DCP:

  • Vastly improved security (ContentAuthenticator)
  • Non-broken and non-brittle subtitle and caption tracks
  • 3D subtitles (eventually)
  • Wider range of framerates
  • Composition metadata (probably no vendor will implement this server-side for Interop)

If security matters at all for the content you are handling for your clients that first bullet point alone should be enough to transition towards SMPTE DCP as soon as possible:

Be aware that Interop systems have no standardized way to enforce valid signature of a composition’s XML from a KDM’s point of view. So you can simply remove a composition’s signature, modify the composition and still playback with the KDM which, in turn, was issued for a specific signed composition.

Ask your clients if they are up for that. It’s like asking Fox whether they would be okay with you screening a self-made condensed version of Avatar. With SMPTE DCP, in combination with a specific KDM formulation, this scenario is impossible.

Also: The vendors of DCI systems need the pressure from authoring and exhibition to iron out bugs and quirks in their SMPTE implementations. Compliance certification goes a long way towards that. But the actual systems in the field need proper feedback from all of us.

All that to the benefit of the initial vision of digital cinema: To provide a common platform for films to play anywhere in the world, be it in Anchorage or in Zhengzhou. Interop DCP won’t help much more towards that goal.

FAQ Contents

Festivals in the age of digital

Lots of filmmakers are asking about DCP. What can I tell them?

Festivals today are in a tough spot. With wider access to DCP authoring tools the variety of quirks, defects and creative outbursts has increased along. Here’s a list of good practices and no-no’s (in progress and so far in no particular order) for filmmakers who intend to submit home-authored DCPs to festivals.

Good practices include:

  • Festival technicians may be confronted with hundreds of submissions. What might be the result of five years worth of sweat and tears on your part is an item on a long list to them. Give them a fighting chance to solve the many riddles they are facing when prepping for the festival run:
    • The festival schedule might be in-progress
    • The festival schedule might contain english version film titles only. Or not
      Clearly label your DCP. Adhere to standards. If unsure ask someone who is aware of the requirements.
  • Use a validation tool to inspect and check your final package. See dcp_inspect for an open source/free tool to do it.
  • Use the Digital Cinema Naming Convention to annotate and name your compositions and packages. E.g. for a title like “Der Fluss war einst ein Mensch” (BRD 2011, Jan Zabeil) use the first 14 characters as ContentTitle particle: “DerFlussWarEin”. Do not make an acronym out of the real title (like “DFWEEM”) or even — as in this case — “TRUTBAM” which might be an acronym of the title’s albanian translation, for what it’s worth. Noone will have a clue what this thing is. The last thing you want is festival techs having to guess.
  • If you are using Fraunhofer’s easyDCP Creator tool make sure to replace the default ContentTitle and package annotation. Otherwise your package and composition will show up on servers as “easyDCP Creator+ Project (2013-01-02T12:34:56)” and “easyDCP Creator+ Composition 1 (2013-01-02T12:34:56)”. Again noone will have a clue what this thing is.
  • Create a proper cinema sound mix. L/R-only might do on a laptop. It definitely won’t in a cinema. Sweet spots can be tiny in a cinema. L/R-only mixes will mean
    • that people in the sweet spot will hear stuff that’s supposed to come from center (dialogue) coming from everywhere instead
    • that the left half of the audience will hear everything from the left side only
    • that the right side of the audience … well, you get the point.
  • Label your distribution medium properly:
    • Full, exact and unabridged ContentTitleText of all compositions on the medium, e.g.
      FooBar_FTR_F_EN-FR_INT-NO_51_2K_ABC_20131127_EFG_SMPTE_OV
    • Exact runtime lengths of all compositions on the medium
    • Full, exact and unabridged film title in its original language — Not the value of ContentTitleText but the true original title of the film
    • Full, exact, unabridged and relevant language version film titles — Again not the the value of ContentTitleText but the true version titles of the film
    • Audio language versions: Which languages? Subtitles: Which languages?
    • Picture dimensions: 2048×858 or 4096×1716 or 1998×1080 or 3996×2160. If your images are letter- or pillarboxed note the details. Also note explicitly 1920×1080 when your images are actually HD resolution rather than 2K. It matters on screens where the projector is positioned off-center
    • Plaintext or encrypted? Make it clear whether playback of any given composition will require a KDM and, if so, where to call should these be missing, fail to work etc.
    • Contact information (email and mobile phone)

No-no’s:

  • Do not use pocket drives which need 2 USB plugs (data and power). Chances are the recipient will have to copy your package to a proper medium or even reject your drive.
  • Do not add DCSubtitle to the one and only composition in your package when it has burned-in subtitles. Duh.

FAQ Contents

Color and gamma

When I look at my digital cinema compliant JPEG2000 files the colors look strange | odd | wrong

[tbw]

FAQ Contents

Encryption, certificates and key delivery messages (KDMs)

What is a KDM?

KDM is an acronym for Key Delivery Message and it does pretty much exactly that: Deliver 1 or more content keys to a target device. The content keys delivered will be referenced by a specific composition. In addition it tells target devices about the validity range for the delivered content keys. Meaning from when to when devices are allowed to use those content keys.

KDMs are required to be digitally signed.

A KDM is often referred to as the key for a certain composition. While true in the general sense technically that model is not quite on the money.

What is a dcpdig file?

When creating an encrypted DCP with Fraunhofer’s easyDCP Creator+ the app will store plaintext content keys (sic) and key IDs in a DCP digest or dcpdig. These files are XML and look like this:

<?xml version="1.0" encoding="UTF-8"?>
<FHG_DCP_DIGEST xmlns="http://www.fhg.de/2009/04/02/dcpdig">
	<InteropMode>true</InteropMode>
	<CompositionList>
	<Composition>
		<Id>urn:uuid:d69d15ed-82dc-4c12-afc4-72a0a5038f70</Id>
		<ContentTitleText>Foo</ContentTitleText>
	<ReelList>
	<Reel>
		<Id>urn:uuid:202c6d7b-86f6-4107-883a-f414356676c8</Id>
	<MainPicture>
		<Id>urn:uuid:049cc95b-6e14-4fff-ac4b-950a0fb47362</Id>
		<KeyId>urn:uuid:18bc20f2-df27-46d9-89a6-df869826f097</KeyId>
		<Key>1409f66d036766b6487302d7b86e712b</Key>
	</MainPicture>
	<MainSound>
		<Id>urn:uuid:24dd593e-2512-4813-abef-68f1364e98da</Id>
		<KeyId>urn:uuid:1e5b72e9-74a6-4ddf-946a-fd6ccc575b3e</KeyId>
		<Key>d5708d1d56279e8126ee190fd913c538</Key>
	</MainSound>
	</Reel>
	</ReelList>
	</Composition>
	</CompositionList>
</FHG_DCP_DIGEST>

The format is used exclusively by Fraunhofer’s apps.

FAQ Contents

Subtitles

Where can I get TI’s font compressor utility?

See Texas Instruments’ DLP Cinema Technical Documents for Font Compressor Utility (zip).

FAQ Contents