03-11-2012, 01:48 PM
TECHNICAL SEMINAR REPORT ON MPEG-7
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INTRODUCTION
The Moving Pictures Experts Group abbreviated MPEG is part of the International Standards Organization (ISO), and defines standards for digital video and digital audio. The primal task of this group was to develop a format to play back video and audio in real time from a CD. Meanwhile the demands have raised and beside the CD the DVD needs to be supported as well as transmission equipment like satellites and networks. All this operational uses are covered by a broad selection of standards. Well known are the standards MPEG-1, MPEG-2, MPEG-4 and MPEG-7. Each standard provides levels and profiles to support special applications in an optimized way.
It's clearly much more fun to develop multimedia content than to index it. The amount of multimedia content available -- in digital archives, on the World Wide Web, in broadcast data streams and in personal and professional databases -- is growing out of control. But this has led to increasing difficulties in accessing, identifying and managing such resources due to their volume, complexity and a lack of adequate indexing standards.
MPEG-7 is being developed by the Moving Pictures Expert Group (MPEG) a working group of ISO/IEC. Unlike the preceding MPEG standards (MPEG-1, MPEG-2, and MPEG-4) which have mainly addressed coded representation of audio-visual content, MPEG-7 focuses on representing information about the content, not the content itself. The goal of the MPEG-7 standard, formally called the "Multimedia Content Description Interface", is to provide a rich set of standardized tools to describe multimedia content.
A single standard which can provide a simple, flexible, interoperable solution to the problems of indexing, searching and retrieving multimedia resources will be extremely valuable and widely deployed. Resources described using such a standard will acquire enhanced value. Compliant hardware and software tools capable of efficiently generating and interpreting such standardized descriptions will be in great demand.
DIFFERENT VIDEO FORMATS
PC users will almost certainly remember the first time they were able to view a video clip on their computer. The clips were about the size of a postage stamp and were generously referred to as "multimedia". Later, the first acceptable video clips were used in the opening scenes of computer games. In some cases, there were even digital 3D animations that couldn't be created in real-time with the hardware and software that was available in those days. As the video clips demanded extensive storage space (despite their short length), they were only available on CD-ROM drives that had recently become popular. Because of this, many PC's became multimedia-compatible, in a restricted sense, by the integration of a CD-ROM drive and a soundcard. However, their limitations soon became apparent: it wasn't possible to run the video clip smoothly in fullscreen mode even with the most powerful hardware available. With the development of high performance graphic chips, faster processors and corresponding software interfaces, today's users are now able to run video clips in all the usual formats (including fullscreen mode) without problems. We'll continue with a look at the most video formats and we'll then provide an overview of their specific applications.
The AVI Format
One of the oldest formats in the x86 computer world is AVI. The abbreviation 'AVI' stands for 'Audio Video Interlaced'. This video format was created by Microsoft, which was introduced along with Windows 3.1. AVI, the proprietary format of Microsoft's "Video for Windows" application, merely provides a framework for various compression algorithms such as Cinepak, Intel Indeo, Microsoft Video 1, Clear Video or IVI. In its first version, AVI supported a maximum resolution of 160 x 120 pixels with a refresh rate of 15 frames per second. The format attained widespread popularity, as the first video editing systems and software appeared that used AVI by default. Examples of such editing boards included Fast's AV Master and Miro/Pinnacle's DC10 to DC50. However, there were a number of restrictions: for example, an AVI video that had been processed using an AV Master could not be directly processed using an interface board from Miro/Pinnacle.
Apple's Format
The MOV format which originated in the Macintosh world, was also ported to x86 based PC's. It is the proprietary standard of Apple's Quicktime application that simultaneously stores audio and video data. Between 1993 and 1995, Quicktime was superior to Microsoft's AVI format in both functionality and quality. The functionality of the latest generation (Quicktime 4.0) also includes the streaming of Internet videos (the realtime transmission of videos without the need to first download the entire file to the computer). Despite this, Apple's proprietary format is continually losing popularity with the increasing use of MPEG. Video clips coded with Apple's format are still found on some CD's because of Quicktime's ability to run on both Macintosh and x86 computers.
MPEG Formats
The MPEG formats are by far the most popular standard. MPEG stands for "Moving Picture Experts Group" - an international organization that develops standards for the encoding of moving images. In order to attain widespread use, the MPEG standard only specifies a data model for the compression of moving pictures and for audio signals. In this way, MPEG remains platform independent. One can currently differentiate between four standards: MPEG-1, MPEG-2, MPEG-4 und MPEG-7. Let's take a brief look at each format separately.
The MJPEG Format
The abbreviation MJPEG stands for "Motion JPEG". This format is practically an intermediate step between a still image and video format, as an MJPEG clip is a sequence of JPEG images. This is one reason why the format is often implemented by video editing cards and systems. MJPEG is a compression method that is applied to every image. Video editing cards such as Fast's AV Master or Miro's DC50 or the much more inexpensive Matrox Marvel product series reduce the resulting data stream of a standard television signal from approximately 30 MB/s (!) to 6 MB/s (MJPEG file). This corresponds to a compression ratio of 5:1. However, a standard for the synchronization of audio and video data during recording has not been implemented in the MJPEG format so that the manufacturers of video editing cards have had to create their own implementations.
MPEG-7 Working Groups
Currently MPEG-7 concentrates on the specification of description tools (Descriptors and Description Schemes), together with the development of the MPEG-7 reference software, known as XM (eXperimentation Model). The XML Schema Language was chosen as the base for the Description Definition Language (DDL).
The MPEG-7 Audio group develops a range of Description Tools, from generic audio descriptors (e.g., waveform and spectrum envelopes, fundamental frequency) to more sophisticated description tools like Spoken Content and Timbre. Generic Audio Description tools will allow the search for similar voices, by searching similar envelopes and fundamental frequencies of a voice sample against a database of voices. The Spoken Content Description Scheme (DS) is designed to represent the output of a great number of state of the art Automatic Speech Recognition systems, containing both words and phonemes representations and most likely transitions. This alleviates the problem of out-of-vocabulary words, allowing retrieval even when the original word was wrongly decoded. The Timbre descriptors (Ds) describe the perceptual features of instrument sound, that make two sounds having the same pitch and loudness appear different to the human ear. These descriptors allow searching for melodies independently of the instruments.