Reference model and field trial R Storey (BBC), A Alves, J Ruela, L Teixeira and T Andrade (INESC) ABSTRACT Today's available solutions for the production of digitally compressed TV programmes require successive decoding and re-coding operations due both to the multiplicity of digital formats currently in use for signal acquisition and to technology limitations. This has the consequence of increasing the production costs and of reducing the overall signal quality. The ability of using compression also at the production stage will contribute to improve the overall signal quality and to reduce storage requirements and associated costs. The ATLANTIC project (ACTS 078) is developing a digital studio for the production of TV programmes using the MPEG-2 format throughout the entire process, from the input of the studio to final programme distribution. EXPO '98, the next international exposition to be held in Lisbon, has been identified as an ideal showcase for audio-visual services developed by ACTS projects. The ATLANTIC project will provide basic infrastructures and technology for compressed-based TV programme production and distribution of audio-visual information and entertainment services for the entire EXPO site. This paper describes the studio reference model of the ATLANTIC project and the role ATLANTIC will be playing within the planned demonstrations of ACTS projects at EXPO '98. Keywords: MPEG, editing, news studio, broadcast chain, ATM, TCP/IP, CORBA. INTRODUCTION Digital compression is progressively being used in TV broadcast environments. However and in spite of being well explored in many stages of the TV broadcast chain, in the area of programme production/ editing its introduction is still experiencing some delay. The majority of current solutions for non-linear editing systems accept at the input compressed source material, but have to perform cascaded decoding and re-coding operations during edition. The ability of using compression also at the production stage will avoid this cascaded process, thus contributing to improve the overall signal quality and to reduce storage requirements and associated costs. It is precisely the goal of ATLANTIC to develop the technology, which will allow the use of compression within the studio. Hardware developments, supported by consistent software simulations, will be integrated with commercial equipment to implement the ATLANTIC studio. In addition to the proposal of using the MPEG-2 format throughout the complete broadcast chain, communications between the various equipment inside the ATLANTIC studio are provided by an ATM network. MPEG-2 data is stored and transferred as Packetised Elementary Streams (PES) packets. This format, while constituting a legal MPEG-2 stream, provides an integrated method for transferring control and timing information separately with each individual component of the original programme. Each media is thus stored and processed separately, but maintaining its original compressed format and timing relationships. The main objectives and initial directions of work of the ATLANTIC project have been presented at ECMAST '96 [1]. The present document is an overview and update of that paper. It describes the ATLANTIC studio reference model and its functionality, designed for the production of digitally compressed MPEG-2 TV programmes from originally compressed MPEG-2 material. In addition, it presents the planned showcase of services of ACTS projects related to multimedia content creation and delivery at EXPO '98 and the role ATLANTIC will be playing within that demonstration. THE ATLANTIC STUDIO Objectives ATLANTIC aims at the development of technology for the implementation of a totally MPEG-2 TV production studio. It is the purpose of the consortium to demonstrate the feasibility of performing the editing of TV programmes in the MPEG-2 compressed format with quality and cost effectiveness. To accomplish this goal, software simulations are being conducted to assess the quality of programmes after editing and to evaluate the degree of complexity involved in the development of hardware with the same kind of functionality. The project is developing techniques and equipment currently not available commercially and, where possible, will integrate standard equipment and interfaces. An ATM network will be used as the communications infrastructure, to exchange all kinds of information between the studio equipment. Communications
Network infrastructure
The ATLANTIC ATM network will support permanent and switched Virtual Circuits (VC) connections. A suitable category of service for the transmission of MPEG-2 data inside the studio has been selected; it is foreseen the use of the real time VBR service category, with peak rate allocation of network resources [2]. The need to provide reliable transmission of MPEG-2 streams inside the studio has led to the selection of the TCP protocol to meet this requirement, since this is a mature, widely supported standard; Classical IP over ATM [3] is the current architectural choice. TCP control mechanisms, which include slow start and congestion avoidance, have been optimised for use in best effort networks, where losses occur mainly due to network congestion. In ATLANTIC, since stringent performance guarantees are provided by ATM traffic control and resource allocation policies, losses are mainly due to occasional transmission errors. Therefore, TCP error control is required for retransmission of missing packets, but the normal congestion control mechanisms should be disabled, since their use might severely degrade the QoS (reduced throughput and increased delay). Fast retransmission and recovery operation is now supported by new versions of TCP [4] and this will be adapted for use in ATLANTIC, together with a fine tuning of the critical performance parameters. Moreover, as an additional feature, TCP window mechanism will be used together with the server video pump application to control the source rate.
Application control protocols
CORBA is a distributed processing architecture designed to allow the integration of a wide variety of object systems. The CORBA architecture defines an entity, the ORB (Object Request Broker), that has mechanisms to manage communications between clients and servers. CORBA 2.0, as defined within the scope of the DSM-CC User-to-User protocol, will thus be used for the implementation of the interfaces between the ATLANTIC editing workstation and the server. Basically, there will be clients in the Edit WS side and object implementations in the server side. The granularity of these components is under investigation and will be tightly related to the choices made in the scope of the DSM-CC functionality. CORBA enables the use of different programming languages in the specification of clients and object implementations, preferably object-oriented languages (like C++ or Smalltalk). The selection of the language to be used will depend on the CORBA commercial product chosen. Functional description of the ATLANTIC studio components
Format converter
The role of the Format Converter is to recover the elementary components of incoming MPEG-2 TV programmes and to store them as separate streams of PES packets in the Main Server. System information will also be extracted from the transport stream and will be conveniently stored in master index files in the Main Server together with the MPEG-2 PES data. Each PES packet will contain exactly one access unit and will carry in its header the necessary control and timing information to propagate throughout the studio the relationships among components of the same original TV programme. The Format Converter will possibly have to re-format PES packets, i.e., it will have to convert PES packets with a certain number of access units in PES packets with exactly one access unit. Special actions are implemented in the Format Converter when demultiplexing TS packets with the error flag set in order to minimise the impact these errors may have at a later stage in the studio chain. Transport packets with the error flag set and containing PSI tables are discarded. PSI tables are frequently repeated in a Transport Stream but their content is likely to remain unchanged for a long period. This means that in normal operation, this decision should cause no problems. In all other TS packets received with the transport error flag set, the presence and position of the error will be indicated in the index file, and this information will be used by a software cleaner to conceal the errors. Other type of system information carried both in PSI tables and in TS or PES packet headers, will also be extracted and included in the index files. Main server
Browse track generator
Journalist editing workstation
The Edit WS will allow users to produce their own programmes by creating an EDL. An EDL is a list of the decisions which describe a series of edits. The EDLs are produced in the Edit WS, during an off-line session, and passed to the on-line suite (the real-time Bitstream Switch) to control the conforming of the final edit and to be played out at a given time. The Edit WS has access to the master file system (indexes and description of browse bit stream files), stored in the video server, allowing the user to issue requests for data to the server. Thus the user may select browse versions of MPEG-2 video sequences and audio sequences and to read/save the EDL to a server. The journalist at the Edit WS will be able to preview the edited sequences by running the EDLs over the browse versions of the original MPEG-2 video sequences. The GUI will be implemented with Tcl/Tk. The Tool command language Tcl is a text-based scripting language which provides most of the functionality of high-level languages such as Pascal and C. This functionality includes loops, if-else statements, procedure calls and one dimensional arrays. Tcl was originally written for UNIX workstations but has since been ported onto numerous other platforms including the PC, Apple Macintosh and even CD-I. The source code for Tcl/Tk is widely available and free for copying and modification. Thus the Tcl interpreter may be modified with a minimum of cost. Tcl is already being used to program remote network devices and has a large number of users around the world. One of Tcl's advantages, as mentioned above, is that it can be easily extended by adding new commands. One such extension to Tcl provides the user with an interface to the X11 Windowing system. This extension is known as the Toolkit (Tk) and provides commands to create widgets such as windows, buttons, listboxes, scrollbars, etc. These widgets can respond to input from the keyboard and pointer devices. There will be a 'control software' module, running onthe Edit WS, responsible for monitoring and co-ordinating the operation of all units in the ATLANTIC studio. Programmes will be produced, broadcast and stored in the finished programme server in TS format, when the control software instructs the Edit Conformer to execute the EDL created at the Edit WS. Fig. 1 presents the general structure of the Edit WS environment.
![[Fig. 1]](rsfig1.gif) Fig. 1 - Edit WS: General structure and communication with server. The Edit WS GUI will present the following functionality:
Real-time Edit Conformer
The switch operation is performed in different steps: after being instructed to execute the EDL script, a connection is established with the Main Server to request the bit streams to be switched in due time. Within the video switch, information belonging to a complete coded picture will be transferred every 40ms from the interface buffer to the decoder buffer. The bit streams are then processed according to the EDL. The resulting edited MPEG-2 PES video and audio bit streams, will have consistent time-stamps. The Edit Conformer will change the time-stamps of the MPEG-2 PES, whenever necessary. The systems layer of the switch will be able to manipulate the necessary PES header information (PTS, ESCR, ES rate, etc.) and will reside in the output module of the switch (an MPEG-2 TS multiplexer). The MPEG-2 TS multiplexer will receive the edited video and audio PES streams and will generate the final programme as a compliant MPEG-2 TS. The edited programme is then made available both for outside distribution and for storage in the finished programme TS server. Studio reference model Fig. 2 shows the functional block diagram of the ATLANTIC studio Reference Model.
![[Fig. 2]](rsfig2.gif) Fig. 2 - Small studio reference model using ATM network architecture. Information exchanged among the studio equipment through the ATM network, will be processed by a protocol stack. The upper layers of this stack are distinct for control messages and for MPEG-2 audio-visual information. Fig. 3 presents the corresponding protocol reference model.
![[Fig. 3]](rsfig3.gif) Fig. 3 - Protocol Reference Model. EXPO '98 – COMBINED SHOWCASE OF ACTS PROJECTS Background The SIC chain (Technology for Content Creation) is aiming to establish a solid technical base for multimedia content creation within a core of ACTS projects, in order to support joint trials leading to advanced program production services. An ambitious proposal for integration of project results and their joint presentation during the EXPO '98 is being planned. The next international exposition, to be held in Lisbon, Portugal, from May to September 1998 has been identified as an ideal showcase for the services developed by ACTS projects, especially those related to multimedia content creation and delivery. The theme of EXPO '98 is 'The Year of the Ocean' in keeping with Portugal's great seafaring history. Three factors make it ideal; its timing, which is at the end of the first phase of ACTS projects, the organisers wish to use the event to pioneer new technology, and pavilion space for each nation will be traded for Audio-Visual content. This latter aspect provides a valuable incentive to produce high quality content, which proved very difficult to find at previous EXPOs. Beyond providing an occasion to test the integration of technical results, the influence of the demonstration should persist long after EXPO has closed because it allows the practical validation of interfaces in a real environment. This will lead to solid interface standards, guidelines and working practices which can be proposed to international standards bodies, such as EBU, SMPTE, ETSI, ITU, ATM Forum and DAVIC, as well as the creation of derived MM products illustrating the achievements of the ACTS program. Description of demonstration proposal The demonstration proposition is to provide a showcase for the services developed by ACTS Projects funded by the European Commission. This will show to politicians and the general public the part that EC funding plays in the progression from basic research, through service development to products manufactured by European Industry, and the resulting generation of wealth and increased employment. The influence of this concerted service trial will persist long after EXPO has finished because it provides an opportunity not only to define interfaces between Audio-Visual technologies but also to validate them in a real working environment. Interface standards, guidelines and working practices can then be proposed to international standards bodies with the sure knowledge that they work in practice. The form of the proposed demonstration is an Audio-Visual communications infrastructure through which are provided real-time audio and video delivery services and content creation services, as shown in Fig.4.
![[Fig. 4]](rs49a.gif) Fig. 4 - Configuration of ACTS projects demonstration at EXPO '98. The backbone of the demonstration is an Audio-Visual communications infrastructure provided by Portugal Telecom, offering essential connectivity for full-time and visiting ACTS Projects. The content delivery service provides information and entertainment services for the entire EXPO site. These parts of the demonstration remain in place for the duration of EXPO, subject to adequate funding, since they fulfil the basic role of delivering the messages to their audience. The concept of visiting projects allows more cost-effective exposure of a broader range of ACTS Projects without unduly interrupting their internal workplans. The idea is that different groups of related Projects will be scheduled to appear in an European Commission Pavilion at times amenable to their individual workplans. Each group of projects would visit for one or two weeks, thereby reducing the cost to each project and the disruption to their workplans. Audio-Visual content, data channels and connections for inter-working will be made available from the various servers, sources and networks connected to the backbone. This Pavilion houses a demonstration theatre, separate booths for visiting projects and, where possible, longer term demonstration facilities such as a virtual studio and interactive information terminals. The Pavilion allows live and pre-recorded presentations to be given to the general public, business leaders, politicians and other VIPs, in a controlled and comfortable environment. Full-time infrastructure
The basic infrastructure provided by ATLANTIC and AURORA can be supplemented by technologies and equipment from additional ACTS projects, such as SICMA and DVP, either part-time or full-time, depending upon workplan restriction in the individual projects. These contributions can be separated into two categories, content origination and content delivery. Conventional content for the topical magazine programme is originated from contemporary material provided by RTP and archive material of historical value provided by the Portuguese national archive, the latter being pre-processed by AURORA. There will also be pre-prepared material and material contributed from remote locations via ATM. There is also a requirement for EXPO originated content to be distributed around the host country by ATM. In addition to this material it is intended to demonstrate new technologies for content creation currently under development in ACTS projects (e.g., virtual edit suite, distributed virtual studio, copyright protection, etc.). Besides the ATLANTIC transmission server, the integration of an interactive continuous media server from SICMA, connected via the ATM network, allows pre-programmed delivery of the different national content contributions interleaved with information items to the pavilions. The use of MPEG-2 compression from ATLANTIC significantly increases the amount of material that can be stored and delivered from a given server and network capacity. This would demonstrate the power of networked delivery of compressed signals by providing high quality audio-visual material for the entire site from one or two servers. The alternative, using present day technology, would require over a hundred manually operated professional videotape machines with the associated capital and staffing costs. FINAL REMARKS This document describes the objectives of the ATLANTIC project and the work in progress, thus providing an overview and update of a paper presented at ECMAST '96. It also presents the current proposal of a combined demonstration at EXPO '98 of audio-visual services developed by a group of ACTS projects, in which ATLANTIC will have an important role. ACKNOWLEDGEMENTS This work has been possible thanks to the support from the EC ACTS programme. The partners of the ATLANTIC consortium are: BBC R&D (UK), CSELT (IT), EPFL (CH), ENST (FR), FhG (D), INESC (PT) and Snell & Wilcox (UK). The authors would also like to extend their acknowledgements to Dr. Nick Wells for his key role as the technical leader of the ATLANTIC project and to Dr. Colin Smith and Dr.Brendan Slamin for their major contributions in the preparation of the EXPO '98 proposal. REFERENCES
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