David K. Fibush

Timing and Synchronization Using MPEG-2 Transport Streams

MPEG-2 transport streams are being applied throughout the world to deliver compressed audio and video, in addition to data and control signals. An understanding of the timing and synchronization of compressed television is important to system design and operations, just as it is with todays full-bandwidth signals. This paper describes the formation of the transport stream with its timing elements and their use at the receiver. It also briefly describes test equipment that has been developed to stress the receiver reference clock phase-locked-loop and to analyze transport stream data to determine the values and correctness of the various time stamps.

Practical application of objective picture quality measurements

Increasing use uncompressed video methods in the generation and distribution of television programs has led to a requirement for objective picture quality measurement methods. Although traditional, indirect, signal quality measurements are still required for evaluation of the uncompressed part of the system, they are not adequate for evaluation of the compression-decompression process. Subjective testing methods are complex, time consuming, and only applicable for development purposes. They do not lend themselves to operational monitoring, production line testing, or trouble shooting. Considering the variety of video compression methods and growing ease of data interconnection, measurement of the resulting video quality must not be limited to a particular compression system. This paper describes the feature-extraction and picture-differencing objective picture quality measurement methods with reference to ongoing research developments. Emphasis is placed on application of the human visual system model to picture-differencing as the preferred objective method. System requirements for application of the model are described in conjunction with a practical implementation of a measurement set.

Testing multimedia transmission systems

Digital television and the convergence of television and telecommunications challenges the television engineer to develop new test methods and new ways of using older methods. Supporting multimedia capabilities makes compressed data transmission an important issue. This article outlines a layered model for systems and testing analogous to the OSI model for communications systems and discusses specific test methods for analysis and generation.

Aspects of Testing in Modern Television Systems

In the past 50 years, methods of testing television systems have progressed from the use of general purpose oscilloscopes to a well-defined set of measurements using television-specific instruments. Introduction of digital techniques into the traditional analog television system, over the past 15 years, has increased the range of specifications to be evaluated but has not changed the basic testing paradigm for video, indirect measurement using test signals. Although there are many useful compression algorithms, MPEG-2 appears to be the most universal, along with its widely accepted system definition for the transmission of additional data encountered in multimedia applications. Introduction of practical video compression techniques has added a whole new dimension to video measurement methods, the need for instruments to directly measure picture quality. The MPEG-2 transport stream, with its small packets, was developed for transmission systems and can be used to carry all types of data. This paper outlines a layered model for systems and testing analogous to the open systems interconnection (OSI) model for communications systems. Methods of picture quality measurement are discussed followed by a description of the MPEG-2 transport stream and test methods for its analysis and generation.

Digital-to-Analog Conversion — Data and Filter Requirements

Ringing in the analog waveform caused by the filter response to the converted digital data is not a new problem. Early digital-based character generators for composite television applications caused significant ringing because the digital data produced too sharp an edge in the picture. Due to the specifications of component digital video, these edge effects are once again becoming more apparent in television operations. This paper discusses the results of using 13.5-MHz, luminance sampling to obtain flat analog bandwidth to 5.75 MHz, and how the filter template required by the international standard will inevitably result in some noticeable ringing on fast picture transitions. Data requirements in the digital domain are analyzed using 2-T pulses as an example while suggesting a different edge transition that will produce much less ringing. Designers are advised to consider the application of filters or edge processing to reduce the ringing due to digitally generated signals.

Video Testing in a DTV World

This paper describes the digital television system, its elements, and appropriate methods of video testing. A layered approach is defined including video, protocol, and transmission channel testing. With todays use of video compression there is still a need for traditional analog and full bandwidth digital testing methods. Compression systems require objective picture quality measurements of distortions caused by its nonlinear and time-variant digital processing. Test method terms such as in-service and realtime are defined for loth video and protocol testing. The three internationally accepted system approaches to objective picture quality testing are discussed including the advantages and disadvantages of each.

Overview of standardization activities related to digital television

With the advent of digital television transmission, measurements to insure quality of service have expanded to include models of the human vision system. This paper reviews international and North American broadcast-video standardization activities. A description of the scopes and related work in such organizations as the Society of Motion Picture and Television Engineers, the Institute of Electrical and Electronics Engineers and the International Telecommunication Union provides prospective for the developing field of objective television picture quality measurement methods.