Digital Video: An Introduction to MPEG-2 / Edition 1

by Barry G. Haskell, Atul Puri, Arun N. Netravali

Overview

Digital Video offers comprehensive coverage of the MPEG-2 audio/visual digital compression standard. The treatment includes the specifics needed to implement an MPEG-2 Decoder, including the syntax and semantics of the coded bitstreams. Since the MPEG-2 Encoders are not specified by the standard, and are actually closely held secrets of many vendors, the book only outlines the fundamentals of encoder design and algorithm optimization.

Product Details

ISBN-13:	9780412084119
Publisher:	Springer US
Publication date:	12/31/1996
Series:	Digital Multimedia Standards Series
Edition description:	2002
Pages:	441
Product dimensions:	6.10(w) x 9.25(h) x 0.36(d)
Age Range:	18 Years

Read an Excerpt

Chapter 2: Anatomy of MPEG-2

As you may have guessed by this time, the MPEG-2 Video standard specifies the bitstream syntax and decoding process not only for single layer (MPEG- 1 like) video coding but also for scalable video coding. Scalability is the property that allows decoders of various complexities to be able to decode video of resolution/quality commensurate with their complexity from the same bitstream. We will discuss a lot more about MPEG-2 scalable video coding in Chapter 9, but for now we illustrate the general principle by introducing the generalized scalable codec structure shown in Fig. 2.3. In MPEG-2 Video there are many different types of scalability and thus it is difficult to represent all of them with a single generalized codec. Our generalized codec structure basically implies spatial and temporal resolution scalability.

Input video goes through a Pre-Processor that produces two video signals, one of which (the Base Layer) is input to an MPEG- 1 or MPEG-2 Nonscalable Video Encoder and the other (the Enhancement Layer) input to an MPEG-2 Enhancement Video Encoder. Some processing of decoded video from MPEG- 1 or MPEG-2 Nonscalable Video Encoder may be needed in the Mid-Processor depending on specific scalability. The two bitstreams, one from each encoder, are multiplexed in Sys Mux (along with coded audio and user data). Thus it becomes possible for two types of decoders to be able to decode a video signal of quality commensurate with their complexity, from the same encoded bitstream. For example, if an MPEG-1 or MPEG-2 Nonscalable Video Decoder is employed, a basic video signal can be decoded. If in addition, an MPEG-2 Enhancement Video Decoder isemployed, an enhanced video signal can be decoded. The two decoded signals may undergo further processing in a Post-Processor.

Since the MPEG-2 Video standard, to be truly generic, had to include a bitstream and semantics description for a variety of coding methods and tools, the implementation of all its features in every decoder was considered too complex and thus the standard was partitioned into Profiles. In MPEG-2 Video, applications with somewhat related requirements are addressed via Profiles; a Profile typically contains a collection of coding techniques (or tools) designed to address a set of such applications. We will discuss a lot more about Requirements and Profiles in Chapter 11.

The MPEG-2 Video standard is a syntactic superset of the MPEG-1 Video standard and is thus able to meet the requirement of forward compatibility, meaning that an MPEG-2 video decoder should be capable of decoding MPEG- 1 video bitstreams. The requirement of backward compatibility, meaning that subsets of MPEG-2 bitstreams should be decodable by existing MPEG- 1 decoders, is achieved via the use of scalability and supported in specific profiles. To confirm that the MPEG-2 Video standard met its quality objective for various Profiles and for individual applications within a profile, a series of verification tests have been conducted in association with other international standardization bodies and a number of organizations. Thus far, these tests confirm that MPEG-2 Video does indeed meet or exceed the performance bounds of its target applications. MPEG-2 Video quality has also been judged sufficient for HDTV34 Recently, newer applications of MPEG-2 Video have also emerged, necessitating combinations of coding tools requiring new Profiles.

At the time of writing of this chapter in early 1996, two new amendments in MPEG-2 video, each adding a new profile, are in progress. One of the two amendments is nearly complete, and the second one is expected to be completed by the end of 1996. Although MPEG-2 video already includes various coding techniques (decoding techniques, really), in reality, these techniques must be included in one of the agreed Profiles also (these profiles can even be defined after completion of the standard). Next, we briefly introduce what application areas are being targeted by these two amendments.

The first amendment to MPEG-2 Video involves a Profile that includes tools for coding of a higher resolution chrominance format called the 4:2:2 format. We will discuss more about this format in Chapter 5; for now, we need to understand why it was relevant for MPEG-2 video to address applications related to this format. When work on MPEG-2 Video was close to completion, it was felt that MPEG-2 video was capable of delivering fairly high quality, and thus it could be used in professional video applications. In sorting out needs of such applications, besides higher bitrates, it was found that some professional applications require higher than normal chrominance spatial (or spatiotemporal) resolution, such as that provided by the 4:2:2 format while another set of applications required higher amplitude resolution for luminance and chrominance signal. Although coding of the 4:2:2 format video is supported by existing tools in the MPEG-2 Video standard, it was necessary to verify that its performance was equal to or better than that of other coding schemes while fulfilling additional requirements such as coding quality after multiple codings and decodings.

The second amendment to MPEG-2 Video involves a Profile that includes tools for coding of a number of simultaneous video signals generated in imaging a scene, each representing a slightly different viewpoint; imaging of such scenes is said to constitute multiviewpoint video...

Table of Contents

to Digital Multimedia, Compression, and MPEG-2.- Anatomy of MPEG-2.- MPEG-2 Systems.- Audio.- Video Basics.- Digital Compression: Fundamentals.- Motion Compensation Modes in MPEG.- MPEG-2 Video Coding and Compression.- MPEG-2 Scalability Techniques.- Video Stream Syntax and Semantics.- Requirements and Profiles.- Digital Video Networks.- Interactive Television.- High-Definition Television (HDTV).- Three-dimensional TV.- Processing Architecture and Implementation.- MPEG-4 and the Future.