What is a DCP format?
Digital Cinema Package
A (Digital Cinema Package)DCP format is a collection of Video and Audio MXF(Material eXchange Format) files for streaming of the media on the Cinema/Projection Server. These MXF file acts as file wrappers which contain the image/video and the audio files in a compressed format to reduce the size of the file and transported in the most efficient manner.
It is a container file similar to MOV or AVI. These files can also be encrypted to avoid unauthorized access to the data.
The images file consist of the image -JPEG2000 file format and audio- 24-bit Linear PCM channel.
A DCP package consists of additional files along with the audio and video files which acts as supporting file and which run concurrently with the audio and video MXF files to provide information as to how this file will be running from beginning to end.
What is the J2k Format?
J2k refers to JPEG2000. This is an image compression format required for screening of the Ad Films/Ad Commercial in Theater. J2k conversion is the last step in the post-production process. After the editing is complete and the movie is exported from the editing timeline, it has to l undergo the final step in the post-production process wherein, it is converted into another format called JPEG2000 format to make it compatible with the cinema server for screening in the theater and multiplexes.
The process remains same, be it a Slide, an Ad Film, Ad Commercial, Documentaries, Feature Film, Commercial or Art Films. A typical movie can either be screened through a Satellite service like the UFO format or the J2k Format. Since the cost involved in broadcasting is pretty high using the UFO format, J2k DCP format become the only ideal and the best solution for small scale players in the market.
These Six Files mentioned below are part of the DCP format :
1) Video/Image MXF File
2) Audio MXF File
3) Asset Map File
4) Composition Playlist File(CPL)
5) Packing List File(PKL)
6) Volume Index File
Let us now discuss some technical specification for these files to get a more detailed understanding of the DCP package :
1) Video/Image MXF File
The Video/Image file is basically a J2C more commonly know as J2K(JPEG2000) image sequence which is wrapped in MXF file container.In certain theater, MPEG2 format technology is still being used, wrapped in the MXF container. However, it is no longer complaint with DCI(Digital Cinema Initiatives) specifications , but is still acceptable in some theaters as video format for screening.
We will not get into the details of MPEG2 format specification as this is out of the scope of this article.
There are two industry standard followed :
b) MXF INTERLOP
Now, at most places, the SMPTE standard is accepted. MXFINTERLOP is used rarely. The standard should be checked with the Cinema Theater for screening. They will surely provide the details of the DCP for their Cinema Projection Screen.
Lets us now get an understanding of Frames used :
Frame Rates :
• 24, 25, 30, 48, 50, and 60 fps for a 2K screening
• 24, 25, and 30 fps for a 4K screening
• 24 and 48 fps for a 2K stereoscopic
JPEG2000(MXF INTERLOP STANDARD)
• 24 and 48 fps for 2k Screening
• 24 fps for a 4K screening
• 24 fps for a 2K stereoscopic screening
As discussed earlier also , this format is not much in use ,however the frame rate for these are :
• 23.976 and 24 fps for 1920 × 1080 or a 2K screening
Frame Size and Aspect ratios:
• Flat Container (1998 x 1080 for 2K and 3996 x 2160 for 4k) :Aspect Ratio :1.85:1
• Scope Container(2048 x 858 for a 2K and 4096 x 1716 for a 4K): Aspect Ratio : 2.39:1
• Full Container (2048 x 1080 for a 2K and 4096 x 2160 for a 4K) : Aspect Ratio : 1.9 :1
• Full Frame (1920 x 1080)
• Pixel Depth : 12bits per pixel(12x3=36 bits in total )
• XYZ Color Space
The maximum bit rate at which it the files will be transcoded is 250 Mbit/s at 24 Frames/s. Above this the frames will start dropping. Remember that the file will become heavy ,requires more storage space also.
2) Audio MXF File
The Audio file is created separately as an MXF File that runs in synchronization with the Video MXF file.
The Linear PCM file created has the following details :
• The Sound channel can be distributed as Stereo File (2.1) or 5.1 or 7. 1 Channel.
• Bit Depth - 24 bits
• Sample Rate -48000 Hz or 48 kHz for a Cinema screening
• Multi Mono Files.
• Bit Rate Mode : Constant
• Bit Rate : 6912 kb/s
• So, lets say if we are creating a 5.1 Channel System, then we will have the following Multi Mono files:
1. Channel 1 Mono File : Sample.L.Wav
2. Channel 1 Mono File : Sample.C.Wav
3. Channel 1 Mono File : Sample.R.Wav
4. Channel 1 Mono File : Sample.LFE.Wav
5. Channel 1 Mono File : Sample.Ls.Wav
6. Channel 1 Mono File : Sample.Rs.Wav
3) Asset Map File
An Asset map file will list all the files that are created in a DCP in XML format :
4) Composition Playlist (CPL)
This file is also in XML format and consist of sequence in which the playback will be presented on the cinema screen.
5) Package List File (PKL)
All the file are basically Hashed and their Hash is stored in this File. This is file is important at the time of ingestion of the DCP in the cinema server to check for consistency and ensure that the file is not corrupted .
6) Volume Index(VOLINDEX)
This is an XML file to check the volume order of the DCP file created and stored in a hard drive.
Understanding the Color Space system :
The Digital Cinema Package(DCP) created for movie screening uses a different format known as the XYZ Color space. However, the human eye's see the objects in RGB Color space. It is one of the most widely used and acceptable color format compatible for human eye. All the devices that displays the image in this format.
XYZ color space is much more and wider than the XYZ format .XYZ format has much larger scope than RGB format and it can takes colors beyond the RGB spectrum also. The important thing to understand here is that the colors are converted from an RGB space to XYZ space for a DCP cinema screening
Rec709 is the color standard that is used for grading during the creation of the Cinema Package for Digital Cinema Screening.
Settings for Video for Digital Cinema Package,
• A Gamma Offset of 2.2 is used in Rec709 and sRGB color profiles.
• Color Temperature is set at 6500K(Kelvin).
• Bit Depth is kept at 12-bit Color (Which is 4096 colors per channel = Trillions of Colors) or 32 Bit Floating Value.
Encrypting the DCP package:
The DCP package comes with the option of encryption . This is required in order to avoid unauthorized distribution of the commercial film/Ad-films . The (MXF File- audio and video) are encrypted using the AES encryption . Asymmetric 2048 bit RSA is used to encrypt these AES keys . This AES encryption has its own public and private key . The private key is stored with the playback system and the public key is shared the owner/distributor.
After the encryption is done, A KDM(Key Delivery Message) is generated . These KDM's are nothing but an XML file which contains these AES keys which can be played on the destination device only with the private key of the devices. These KDM's also provide the facility of creating time and date limits on the data with projection system on which it will be played, which simply means that the projection system will not be able to play the package outside the time and date defined for that content ,which ensures that the date cannot be played prior or beyond the specified time and date ,thus putting a check on unauthorized distribution of the data.
Delivery of the DCP package:
The DCP package can be delivered on FAT32 or NTFS formatted hard drive. Thi