A High Data Rate Interface for Digital Cinema Equipment By Adrian Widera and Siegfried Foessel
Introduction For many years the HDTV area with single and dual link HD-SDI connections marked the high end of digital data transmission interfaces. Corresponding standards are SMPTE 292M1 with 1.485 Gb/s data rate and SMPTE 372M2 with 2.97 Gb/s. With the introduction of digital cinema the demand on higher bandwidth interfaces for real-time transmission of data appears. This is evident in the acquisition and exhibition process with image sizes from 2 MPixels to 12 MPixels per frame and bit depths of more than 10 Bit for all color components. For acquisition of theatrical motion picture content several electronic cameras have been introduced to the public lately. The potential output capabilities of many of these cameras exceed the data rates of the above mentioned interfaces. The same appears in the exhibition process, where the Digital Cinema Initiatives, LCC (DCI)4 defined 2k and 4k formats. If the movie data is decompressed in a player device and transferred over a link to a projector the data rate on the link exceeds the previous interface limits. Generally interfaces with data rates of 10 Gb/s to 20 Gb/s seem suitable for the digital cinema field. In this article an interface based on standard 10G Ethernet5 is proposed as a solution for real-time interfaces for digital cameras in particular, but also for other areas of digital cinema.
Field of Application The primarily intended field of application for the proposed interface is the connection of electronic digital cinema cameras to appropriate recording devices. Besides that the interface should possibly be suitable for interconnecting digital cinema equipment for postproduction, distribution and presentation. If possible an interface should be used, which is also used in other areas. This guarantees a wider spread, a better availability of devices and accessories and in the end competitively priced systems.
Postproduction
Acquisition
Camera
10Gig Interface
Field Recorder
10Gig Interface
IT-Environment
10Gig Interface
Presentation
Server
Projector
10Gig Interface
Figure 1: High Data Rate Interfaces for Digital Cinema Equipment
Requirements Data Types The main task of the interface is the exchange of essence data in form of image or audio data and associated metadata as well as control information. Whereas control information and
some metadata require a simultaneous, bidirectional communication, it can be assumed that the comparatively huge amount of essence data will only be transferred unidirectional. The different data types should be bit-serialized and multiplexed as shown in Figure 2.
Figure 2: Communication Channel
Bandwidth The camera's estimated potential image output capabilities and resulting data rates for uncompressed, baseband images are given in Table 1. Data rates resulting from DCI image containers and state of the art film scanners are listed as well. Adding a comparatively small amount of data for audio, metadata, control information and transfer mechanisms, an interface providing a sustained data rate of approximately 10 Gb/s is required. The red shaded cells in Table 1 indicate where the capabilities of current industry standard interfaces like SMPTE 292M and SMPTE 372M which are limited to data rates of 1.485 Gb/s and 2.970 Gb/s respectively are exceeded. Furthermore these interfaces generally refer to HDTV content with image raster formats defined in SMPTE 274M3. For digital theatrical motion pictures the highest achievable image quality is expected which leads to higher spatial resolutions, higher bit depths, avoidance of horizontal sub-sampling and eventually results in higher data rates. According to the "DCI, Digital Cinema System Specification"4 image structure containers with resolutions up to 4096 x 2160 pixels and 2048 x 1080 pixels and a bit depth of 12 Bit per component are proposed. In order to provide appropriate overhead for postproduction, spatial and temporal resolution, as well as bit depth might be even higher during acquisition than presentation. Because of the variety of formats and possible payloads e.g. compressed or baseband data, a flexible interface with freely definable image parameters within some given boundaries is needed.
Film Scanner
Cameras
DCI
Source Type
hRes vRes Samp- Frame Data Rate [Gb/s] for Bit Depth of [px] [px] ling Rate 10Bit 12Bit 14Bit 16Bit [fps]
4k
4096
2160
444
24
6,370
7,644
8,918
10,192
2k
2048
1080
444
24
1,593
1,911
2,230
2,548
2k
2048
1080
444
48
3,185
3,822
4,459
5,096
ARRI D-20
2880
2160
444
24
ND
5,375
ND
ND
1920
1080
444
96
ND
7,166
ND
ND
Dalsa Origin
4046
2048
444
24
ND
ND
ND
9,546
2048
1080
444
24
ND
ND
ND
1920
1080
422
24
1,593 0,995
ND
ND
ND
Panavision Genesis
1920
1080
444
50
3,110
ND
ND
ND
1k full aperture
1024
778
444
24
0,574
0,688
0,803
0,918
2k full aperture
2048
1556
444
24
2,294
2,753
3,212
3,671
3k full aperture
3072
2334
444
24
5,162
6,195
7,227
8,260
4k full aperture
4096
3112
444
8
3,059
3,671
4,283
4,895
6k full aperture
6144
4668
444
0,5
0,430
0,516
0,602
0,688
8k full aperture
8192
6224
444
0,1
0,153
0,184
0,214
0,245
Table 1: Estimated Image Data Output Capabilities and Resulting Data Rates
Interface Outline Underlying Technology, Layer Concept 10GE (10 Gigabit Ethernet) technology seems to have the potential to bridge the gap between professional acquisition equipment and IT environments commonly used in postproduction facilities. A layered approach as depicted in Figure 3 should provide the necessary flexibility to separate standard conform implementations from application specific. Application layer Data
Transport layer UDP
Data
UDP Framing
Data
IP Framing
Data
Ethernet Framing
Network layer IP header
UDP
Network interface Ethernet
IP header
UDP
Physical network
Figure 3: Layer Concept of UDP/IP
Physical Layer IEEE802.3ae5 compliant transceiver modules for the physical layer and standard clocking and framing allow utilization of commonly available IT components which is important regarding the cost factor. With the usage of 850nm 10GE standard XFP modules, fibre optic links of 300m length are possible. Various manufacturers offer appropriate modules for prices around 500 USD. Modules and fibres for 1300nm allow considerably longer distances.
Physical Connector The usage of one fibre per direction allows small physical connectors. Where standard optical LC-duplex connectors might be sufficient for in-house i.e. postproduction or presentation equipment, on set recording requires a modified, maybe hybrid harsh environment connector with micro lenses for cleaning purposes and beam expansion.
Connection Type, Protocols and Transport Dedicated point-to-point links and specific data stream protocols make sure that bandwidth and quality of service requirements are met. In case the data rate exceeds the capabilities of a single link a second parallel link analogue to dual link HD-SDI can be applied. It is important to note that especially the camera-to-recorder connection requires a special link rather than a general purpose 10GE interface. Therefore only special protocols might be implemented and compatibility to other existing 802.3 protocol standards might be provided only where needed. For example it makes sense that the recording device supports a wider spectrum of protocols to be downwards compatible to 1GE or even Fast Ethernet equipment for non-real time transfers whereas the camera interface might only provide special streamlined real time protocols.
For the camera-to-recorder interface a UDP/IP protocol as depicted in Figure 4: Data Transport Protocol seems to be appropriate. As shown in Figure 3 source data belongs to the application layer, the UDP header to the transport layer, the IP header to the network layer and the Ethernet header represent the network interface. To minimize protocol overhead and streamline the communication, layer 2 jumbo frames with sizes up to 9000 Bytes should be used. For detection and correction of transmission errors 6B line encoding in combination with CRC-32 (cyclic redundancy check) and an optional FEC (forward error correction) are recommended.
Figure 4: Data Transport Protocol
Conclusion With a 10G Ethernet based interface as point-to-point connection between camera and recorder a technology can be used which will most likely be vastly implemented in the IT industry within the next years. That guarantees lower priced realization possibilities and longterm support for corresponding chipsets and devices. UDP/IP is suited to support appropriately performing point-to-point connections using standard IT components i.e. switches and existing network drivers in computers. As next specification step it is essential to define the payload within the data stream. For this purpose data types for images, audio, metadata and control information shall be specified and standardized.
1
2
3
SMPTE 292M-1998 – Television, "Bit-Serial Digital Interface for High-Definition Television Systems", www.smpte.org SMPTE 372-2002M – Television, "Dual Link 292M Interface for 1920 x 1080 Picture Raster", www.smpte.org SMPTE 274M-2005 – Television, " 1920 x 1080 Image Sample Structure, Digital Representation and Digital Timing Reference Sequences for Multiple Picture Rates", www.smpte.org
4 5
Digital Cinema Initiatives LLC, Digital Cinema System Specification v1.0, July 20, 2005, www.smpte.org IEEE 802.3ae-2002 – " IEEE Standard for Information Technology - Local & Metropolitan Area Networks - Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications - Media Access Control (MAC) Parameters, Physical Layer, and Management Parameters for 10 Gb/s Operation", www.ieee.org
The Authors Adrian Widera
Adrian Widera is Research and Development Engineer at the Electronic Imaging Department of the Fraunhofer IIS (Institute for Integrated Circuits) in Erlangen, Germany. He is presently involved in several projects concerning the development of technologies for a future digital cinema. Adrian finished his studies of Media Technology with a specialization in Media Production at the Technical University of Ilmenau, Germany in June 2004 and holds a degree as DiplomIngenieur (M.Eng. equivalent). He began his career in the professional Film and Video industry as an intern at the Customer Service and Technical Support Department at Avid’s Central European Office in Munich, Germany in Oct 2000. Since then he is working as a freelancer for Avid and several resellers as Customer Service Field Engineer, Technical Support Representative or Instructor.
Siegfried Foessel
Siegfried Foessel is project manager and coordinator for all projects in the field digital and electronic cinema within the Fraunhofer IIS. Siegfried Foessel, born in 1964, received his Diploma degree (MS) in Electronic Engineering from the University of Erlangen, Germany, in 1989. He started his professional career as an engineer at the Fraunhofer Institute IIS in Erlangen. Between 1994 and 2001 he was
responsible for the business fields Industrial Automation Systems, later for Industrial Sensor Systems. Here his work focused on the integration of image processing systems in industrial environments and on the development of new cameras for industrial applications. In 2000 he received his Ph.D. degree from the University of Erlangen for his work on New Distribution Algorithms for Image Processing in Multiprocessor systems. Since 2001 he is project manager and coordinator for all projects in the field digital and electronic cinema within the IIS. Running projects are the development of high-end camera systems like the ARRI D20, the standardisation and implementation of new data compression algorithms for digital cinema (JPEG2000), the development of new field recorder systems as well as the development of new workflows for digital cinema. He is member of ISO SC29, SMPTE, DIN, FKTG and EDCF. Within the ISO SC29 JPEG group he chairs the adhoc group for digital cinema. He is also coordinator of the projects Worldscreen and Cinevision2006.
