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What is a Digital Cinema Distribution Master / DCDM?

A Digital Cinema Distribution Master / DCDM

is a prestage format in the process of creating a DCP / Digital Cinema Package. The DCDM is mostly archieved alongside with the DCP, to act as a source format for future purposes (remastering / ancilliary markets, lokalised versions…)


How does encryption work in digital cinema?

Digital cinema uses a two step encyption method.

Every media asset of an encrypted DCP is encrypted with a 128 bit AES key. This step is a symmetric method, that means for encryption (during mastering of the DCP) and decryption (during playback in the movie theatre) the same key is used.

To transport these media keys safely to cinemas an asymmetrical encryption method (2048 bit RSA) is being used. Asymmetrical encryption uses pairs of keys, consisting of a public and a private key. The message is being encrypted with the public key and can only be decrypted with the private key. The public key can not be used to decrypt the message, meaning it can be safely published / forwarded.

So the AES media keys are sent to cinemas as Key delivery message (KDM), encrypted with the public key of the corresponding projection system and provided with a validity period. There the KDM is being imported on the projector and the media keys are extracted with the private key which is stored securely inside the projector. With the extracted media keys the DCP is being decrypted during playback.

This means that the same DCP goes out to every cinema but there has to be single KDM for  for every projection system that will show the DCP. For any KDM that is generated we have to retrieve the corresponding public key / server certificate of the projection system for which the KDM is valid. For this purpose we maintain a database of all projectors in the field, with the information in which movie theatre and cinema hall the projector is used.

And this is how a Key delivery message looks like in detail:

DigitalCinemaPackage_kdm_example_DCM.pdf


Subtitles in digital cinema

How do subtitles work in digital cinema?

There are 2 options for subtitling in digital cinema:

1 . Subtitles as text information

To minimize the space consumed by a Digital Cinema Package it is possible to store subtitles as text information. This text information is then rendered and displayed by the projector during runtime. There is a special .xml format and scheme in which the text information is stored (for Interop and SMPTE there are two different .xml schemes, CineCanvas™ and SMPTE 429-5  which differ slightly). The text information is stored together with the meta data (e.g. in and out points, text effects like italic or bold, and the text position and direction). It is also possible to use a custom font for the subtitles (TrueType format .ttf)

2. Additional picture version with burned – in subtitles

Another possibility is to master a second picture track with the subtitles in the picture (brun-in). This increases the size of the DCP as a seperate picture version is needed. For 3D Films this is until now (September 2015) the most reliable option. There will be an SMPTE standard for 3D subtitling (with depth information) in text format, but until now it is not yet completely adopted.

It is possible to convert nearly any given subtitle text format into the needed .xml format or make a picture version with subtitles burned in. Please contact us if you need further information.

An example of CineCanvas .xml subtitle format for Digital Cinema Package in .pdf format


Mastering: Which format should I use for my source material?

Picture:

Basically we are able to read / process any digital Picture- or Videofootage.
However, the most secure and most reliable way is to start with still image sequences in .DPX, Cineon or .TIFF file format.

Also, several digital video codecs are accepted, altough most of them have their own peculiarities that can lead to unwanted or even unpredictable results. That´s why we tend to recommend the usage of Avid (e.g. DNxHD or Avid Meridien Uncompressed) or Apple Prores Series Codecs, with any other material it’s necessary to do some further tests to guarantee a smooth workflow.
Complex conversion or transcoding of formats can result in additional costs.

We are able to handle ArriRaw and RedRaw material, but we do not recommend using this format for delivery.

Audio:

We accept sound files in .WAV or .AIF format, one file per channel. Files need to be named properly, e.g. when using 5.1 Surround: Left, Right, Center, Low Frequency Enhacement, Left Surround, Right Surround. Interleaved files are also accepted but need to have the right channel order (L,R,C,LFE,LS,RS). The sound files need to have exactly the same duration as the picture. We can also handle Protools project files. We strongly recommend using 5.1 or 7.1 mixing. If you deliver Stereo material we can do an upmix to 3.1 for you.

As a result of films being shot with 25 frames per second it gets more and more necessary to adjust the audiofootage to match these, as adjusting picture frame rates results in unacceptable loss of quality.

There are several ways to adjust the audiofootage:

1. Pitch the whole  material by -4%: Offers best quality with minimal effort.
The disadvantage lies in a slight change of tune that is not noticeable by the majority of the audience. Yet it may be a problem with a composed score. Also you might not be allowed to do this because of a copyright infringement concerning used licensed music.

2. Redo the whole mixing for 24 fps (either by your sound designer or by Digital Cinema Mastering): Best possible quality but high effort and cost. May be the only option with licensed music.

3. Pitch the whole material by -4% without Change in Tune by using special Protools Plugins: Good quality, works well for dialogs and effects, doesn’t work for music. May be a good compromise between cost and quality.

Accepted  Data carriers:

We accept the data on Harddrives (any file system). We recommend to use a fast interface like USB 3.0 or eSATA.

BluRays and DVDs are an option for smaller projects, we recommend to send 2 versions of every disc as these formats are not absolutely reliable.

HDCAM SR / Digibeta need to be imported in to an editing programme which might cause addtional costs.

35mm footage has to digitalised by a third party.


Digital Cinema Package on a CRU DX 115 carrier

What is a Digital Cinema Package / DCP ?

A Digital Cinema Package (abbr. DCP) is a digital filmprint, with a special data format for picture and sound.

Information on prices and procedure of the DCP creation at Digital Cinema Mastering can be found in our pricelist.

The specifications for it have been set by the Digital Cinema Initiatives, a cooperation of 7 big Hollywood studios in the “Digital Cinema System Specifications”. The aim was to set up one standard for digital cinema preventing concurrence of different formats which would have made things a lot more complicated when distributing a film world wide. Another goal was to set up a standard with a high security against piracy. The DCI standard is now widely accepted as the successor of 35 mm film, because its open standard, the absence of any license fee, the high security level and the superior image and sound quality.

Digital Cinema Packages of feature films are mostly delivered via Harddrives, for trailers and ads the distribution via USB flash drives, DVD-ROM or internet download is also possible.

A DCP consists of the media files, a packing list (PKL) and one or more composition playlists (CPL). The information which picture and sound file go together and in which order they sould be played is contained in these composition playlists. Also, if present which subtitles should be shown. So it is possible to store several language versions in one DCP without having to save the redundant information (e.g the picture files) twice, enabling an efficient usage of disk space. Depending on the bitrate a Digital Cinema Package consumes about 1,5 to 2 GB of storage space per minute of duration.

DCP files

Files contained in a DCP.

The picture information is being stored as JPEG 2000 compressed still images in a 12 bit X’Y’Z’ colour space.

Sound information is stored uncompressed in up to 24bit sampling depth and 48 or 96 KHz sampling rate. File format for both is  .MXF .

Subtitles have to be converted to the Texas Instruments CineCanvas (C) format and are stored as .XML files.


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