Digital Cinema Package

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A Digital Cinema Package (DCP) is a collection of digital files used to store and convey Digital cinema (DC) audio, image, and data streams.

数字电影包是一种数字文件集，用于存储和转换数字影像的音频、图像和数据流。

The term has been defined by Digital Cinema Initiatives, LLC in their recommendations for packaging of DC contents. General practice adopts a file structure that is organized into a number of usually multi-gigabyte size Material eXchange Format (MXF) files, which are separately used to store audio and video streams, and auxiliary index files in XML format.

该术语由数字电影倡导联盟（DCI）在对数字影像的打包建议中做出过定义。通用惯例采用一种文件结构来组织成多个通常有几个G大小的MXF文件，这些文件分别用来存储音频和视频流，以及XML格式的辅助索引文件。

The MXF files contain streams that are compressed, encoded, and encrypted, in order to reduce the huge amount of required storage and to protect from unauthorized use. The image part is JPEG 2000 compressed, whereas the audio part is linear PCM. The adopted (optional) encryption standard is AES 128 bit in CBC mode.

MXF文件包含有压缩、编码和加密的数据流，以此来减少所需的大量存储空间和防止未授权使用。图像部分是JPEG 2000压缩文件，然而音频部分是线性PCM（脉冲编码调制）。采用的加密标准是CBC模式中的AES-128位。

The newer SMPTE standards are used to conform the recommendations among different tool vendors and producers. Interop, the legacy DCP standard, is still required to be supported by DCP players.

较新的SMPTE标准用于使不同工具厂商和制片商的建议保持一致性。遗留的DCP标准仍需要各DCP播放器支持。

Technical specifications

技术说明书

The DCP root folder (in the storage medium) contains a number of files, some used to store the image and audio contents, and some other used to organize and manage the whole playlist.

DCP根目录（存储介质里）包含有几个文件，有些用来存储图像和音频内容，有些用来组织和管理整个播放表单。

Picture MXF files

图片MXF文件

Picture contents may be stored in one or more reels corresponding to one or more MXF files. Each reel contains pictures as MPEG-2 or JPEG 2000 essence, depending on the adopted codec. MPEG-2 is no longer compliant with the DCI specification. JPEG 2000 is the only accepted compression format.

图片内容可能存储在与MXF文件相关的一个或多个卷里。每个卷里包含有类似MPEG-2或JPEG 2000 精髓的图片，这要看采用什么样的编码方式。MPEG-2不再与DCI规格相兼容，而JPEG 2000是唯一接受的压缩方式。

Supported frame rates are 24, and 48 frames per second. DCPs conforming to older specifications could be encoded at 25fps. This is now outdated.

Maximum frame size is 2048x1080 for 2K DC, and 4096x2160 for 4K DC. Common formats are:

Flat (1998x1080 or 3996x2160), ~1.85:1 aspect ratio

Scope (2048x858 or 4096x1716), ~2.39:1 aspect ratio

16:9 (1920x1080 or 3840x2160), although not officially supported by the DCI specification, this aspect ratio is commonly used, especially for content originally made for HDTV.

12 bits per pixel precision (36 bits total)

XYZ colorspace

Maximum bit rate is 250 Mbit/s (1.3 MBytes per frame at 24 fps)

支持的帧率为24帧和48帧/秒。和较早规格保持一致的DCP可能是25帧/秒进行编码，不过现在已经过时了。

最大的帧大小：2K数字电影为2048x1080，而4K数字电影为4096x2160。

常见格式为：

纯平（1998x1080 或3996x2160），也就是1.85:1的高宽比

全景（2048x858 或 4096x1716），也就是2.39:1的高宽比

16:9（1920x1080或3840x2160），虽然未被DCI规格官方支持，但是这种高宽比已被广泛使用，特别是用于最初为HDTV制作的内容。

12位/像素的精准度（共36位）

XYZ色彩空间

最大比特率为250 Mb/s（24fps下为1.3MB/s）

Sound MXF files

声音MXF文件

Sound contents are stored in reels, too, corresponding to picture reels in number and duration. In case of multilingual features, separate reels are required to convey different languages. Each file contains linear PCM essence.

声音内容也是以卷的方式存储，在数量和位置上和图片的卷相关。是多种语言的情况下，需要有单独的卷来传输不同的语言。每个文件都包含有线性PCM精髓。

Sampling rate is 48,000 or 96,000 samples per second

Sample precision of 24 bits

Linear mapping (no companding)

Up to 12 independent channels.

采样速率为48000样本或96000样本/秒

采样精准度为24位

线性映射（无压缩）

多达12个独立通道。

Asset map file

安排映射文件

List of all files included in the DCP, in XML format.

DCP中所有文件的列表以XML格式存储

Composition playlist file

编写播放列表文件

Defines the playback order during presentation. The order is saved in XML format in this file; each picture and sound reel is identified by its UUID. In the following example, a reel is composed by picture and sound:

在放映时规定回放顺序。这个顺序被以XML格式保存这个文件中；每个图像和声音的卷都有由它们独有的UUID来区分。下面的例子中，一个卷中包含了图像和声音。

<Reel>

</MainPicture>

</MainSound>

</AssetList>

</Reel>

Packing list file

打包列表文件

All files in the composition are hashed and their hash is stored here, in XML format. This file is generally used during ingestion in a digital cinema server to verify if data have been corrupted or tampered with in some way. For example, an MXF picture reel is identified by the following <asset> element:

所有文件都被散列处理过，而散列函数以XML格式存储下来。通常，该文件在注入数字电影服务器时来认证数据是否以某种方式遭到破坏或者干扰。比如，MXF图片卷被下面的<asset>元素来识别：

<Asset>

<Hash>iqZ3X7TdAjAqniOxT2/hj66VCUU=</Hash>

<Type>application/x-smpte-mxf;asdcpKind=Picture</Type>

</Asset>

The hash value is the Base64 encoding of the SHA-1 checksum. It can be calculated with the command

散列值是SHA-1的Base64校验编码。可以通过命令来计算出来。

openssl sha1 -binary "FILE_NAME" | openssl base64

Volume index file

总索引文件

A single DCP may be stored in more than one medium (e.g., multiple hard disks). This file is used to identify the volume order in the series.

简单的DCP可能存储在不止一个移动介质上（比如，复合式硬盘）。这个索引文件用于识别整个DCP里的文件顺序。

3D DCP

The DCP format is also used to store stereoscopic (3D) contents. In this case, 48 frames per second are used, with frames alternating for left eye and right eye pictures. Since the maximum bit rate is always 250 Mbit/s, this results in a net 125 Mbit/s for single frame, but the visual quality decrease is generally unnoticeable.

DCP格式也用于存储3D内容。此时，使用的是48帧/秒，每帧都分左右两边的图片。由于最大比特率一直是250Mbit/s，对于每帧来说就成了125 Mbit/s，但是通常视觉品质的下降也不是很明显。

DCP creation

DCP制作

Most film producers and distributors rely on digital cinema encoding facilities to produce and quality control check a digital cinema package before release. Facilities follow strict guidelines set out in the DCI recommendations to ensure compatibility with all digital cinema equipment. For bigger studio release films, the facility will usually create a DCDM (Digital Cinema Distribution Master).

大部分制片商和发布商在发布影片之前，依靠数字电影编码设备来生产和用品质控制来检查一个DCP包。硬件设备遵照DCI规格制定的、严格的向导内容，以此来确保所有数字影像设备能够兼容。对于更大些的发布影片，硬件设备通常会创建一个数字影院发布母板（DCDM）。

A DCDM is the post-production step prior to a DCP. The frames are in either DPX or TIFF format and both sound and picture are not yet wrapped into MXF files. A DCP can be encoded directly from a DCDM. A DCDM is useful for archiving purposes and also facilities can share them for international re-versioning purposes. They can easily be turned into alternative version DCPs for foreign territories. For smaller release films, the facility will usually skip the creation of a DCDM and instead encode directly from the DSM (Digital Source Master) the original film supplied to the encoding facility. A DSM can be supplied in a multitude of formats and colour spaces. For this reason, the encoding facility need to have extensive knowledge in colour space handling including, on occasion, the use of 3D LUTs to carefully match the look of the finished DCP to a celluloid film print. This can be a highly involved process in which the DCP and the film print are "butterflied" (shown side by side) in a highly calibrated cinema.

DCDM是在DCP之前的后期制作步骤。所有的帧要么是DPX，要么是TIFF格式，声音和图像还都不能被包裹进MXF文件。DCP可以直接从DCDM编码过来。DCDM对于存档来讲是很有用的，而且对于全球翻拍，硬件设备还可以共享它们。可以很容易地把它们转换成世界各地不同版本的DCP。对于小规模的发布电影，硬件设备通常可以跳过DCDM制作，直接从提供的原始影片的数字源母板（DSM）开始。DSM可能以多种格式和色彩空间提供。因此，编码设备需要广泛地了解色彩空间，其中甚至包括3D LUT的用法来精确地配合。

Less demanding DCPs are encoded from tape formats such as HDCAM SR. Quality control checks are always performed in calibrated cinemas and carefully checked for errors. QC checks are often attended by colourists, directors, sound mixers and other personnel to check for correct picture and sound reproduction in the finished DCP.

很少有DCP从类似HDCAM SR的磁带格式编码过来。品质控制检查在校准影片和差错方面作用非常的大。品质控制检查经常有色彩人员，主管、声音合成人员还有其他检查图像和声音制作的人员参加。

DCP encryption

DCP加密

The AES encryption is applied to all MXF files. The encryption keys are generated and transmitted via a KDM (Key Delivery Message) to the projection site. KDMs are XML files that can be opened only by the destination device. A KDM is associated to each playlist and defines the start and stop times of validity for the projection of that particular feature.

AES加密应用于所有MXF文件。密钥通过KDM生成并传输到投影机上。KDM是只能被终端设备打开的XML文件。KDM和每一个播放列表相关联，规定正确的投影开始和结束时间。

DCP delivery methods

DCP传输方法

The most common method uses a specialist hard disk (most commonly the CRU DX115) designed specifically for digital cinema servers to ingest from. These hard drives were originally designed for military use but have since been adopted by digital cinema for their hard wearing and reliable characteristics. The hard drives are usually formatted in the Linux EXT2 or EXT3 format. NTFS is occasionally used but is generally not considered reliable as some Linux based digital cinema servers (such as those made by Dolby and Sony) are unable to read this format. Hard drive units are normally hired from a digital cinema encoding company, sometimes in quantities of thousands. Drives are commonly shipped in protective hard cases. The drives are delivered via Express Courier to the exhibition site. Other, less common methods adopt a full digital delivery, using either dedicated satellite links or high speed Internet connections.

最常见的方法是使用专门的硬盘（比如CRU DX115），这是为注入数字电影服务器而专门设计的。最初，这些硬盘是用作军事，之后由于它顽强的耐用性和可靠性而被用于数字影院。通常硬盘的格式为EXT2或者是EXT3。有时候也用到NTFS格式，但不是那么可靠，一些LINUX的数字影院服务器（比如Dolby和Sony的产品）就不能读取这些格式。通常，硬盘单元来自某家数字影院编码公司，有时候达到上千的数量。驱动通常通过保护性的硬质箱子运输。通过快递邮寄到放映地点。还有，较少见的是采用完全的数字发放，或者使用专用的卫星连接或者是高速因特网连接.