An Overview of Mpeg Family and Its Applications

This paper presents an overview of the video compression standards related to the MPEG family. MPEG-7 and MPEG-21 are specially covered including its latest standard. MPEG-7 is mainly used for object descriptions and MPEG-21 is for DRM (Digital Rights Management). Keyword: MPEG-1, MPEG-2, MPEG-4, MPEG-7, MPEG-21, MPEG-A, MPEG-D I.INTRODUCTION MPEG is the “Moving Picture Experts Group”, working under the joint direction of the international Standards Organization (ISO) and the International Electro Technical Commission (IEC). This paper will provide an overview of the recent standards in the MPEG family. MPEG-7 is developed for Multimedia content description interface ,it uses XML to store metadata, and can be attached to timecode in order to tag particular events, or synchronise lyrics to a song. MPEG-21 is an open framework for multimedia delivery and consumption. It can be used to combine video, audio, text and graphics. The other latest version in MPEG like MPEG-A, MPEG-D is also discussed in this paper. II. MPEG-1 (1992) MPEG-1 is currently the most compatible format in the MPEG family but does not support interlaced video coding. MPEG-1 typically operates at bitrates of 1.5 Mbit/s with a screen resolution of 352*288 pixels at 25 frames a second [1, 8]. MPEG-1 coded bitstream has been designed to support a number of operations including random access, fast search, reverse playback, error robustness, and editing [1]. A number of techniques are used to achieve a high compression ratio. The first is to select an appropriate spatial resolution for the signal. The algorithm then uses block-based motion compensation to reduce the temporal redundancy. The difference signal, the prediction error, is further compressed using the discrete cosine transform (DCT) to remove spatial correlation and is then quantized. Finally, the motion vectors are combined with the DCT information, and coded using variable length codes. Figure 1 below illustrates a possible combination of the three main types of pictures that are used in the standard. Figure 1 -Example of temporal picture structure. ISSN : 0976-5166 240 S. Vetrivel et. al. / Indian Journal of Computer Science and Engineering Vol. 1 No. 4 240-250 A. Application: It is basically designed to allow moving pictures and sound to be encoded into bitrate or a Compact Disc. It is used on Video CD SVCD and can be used for low-quality video on DVD video [1]. III. MPEG-2(1994) A. Codec structure MPEG-2 is aimed for high bitrate, high quality applications, seen as Digital TV broadcasting and DVD [6]. In an MPEG-2 system, the DCT and motion-compensated interframe prediction are combined, as shown in Fig. 2. The coder subtracts the motion-compensated prediction from the source picture to form a 'prediction error' picture. The prediction error is transformed with the DCT, the coefficients are quantized and these quantized values coded using a VLC. The coded luminance and chrominance prediction error is combined with 'side information' required by the decoder, such as motion vectors and synchronizing information, and formed into a bitstream for transmission. Fig.3 shows an outline of the MPEG-2 video bitstream structure. Fig. 2 (a) Motion-compensated DCT coder; (b) motion compensated DCT decoder . ISSN : 0976-5166 241 S. Vetrivel et. al. / Indian Journal of Computer Science and Engineering Vol. 1 No. 4 240-250 Fig. 3 Outline of MPEG-2 video bitstream structure (shown bottom up). In the decoder, the quantized DCT coefficients are reconstructed and inverse transformed to produce the prediction error. This is added to the motion-compensated prediction generated from previously decoded pictures to produce the decoded output. In an MPEG-2 codec, the motion-compensated predictor shown in Fig. 2 supports many methods for generating a prediction B. Details of non-scalable profiles: Two non-scalable profiles are defined by the MPEG-2 specification. The simple profile uses no B-frames, and hence no backward or interpolated prediction. Consequently, no picture reordering is required (picture reordering would add about 120 ms to the coding delay). With a small coder buffer, this profile is suitable for low-delay applications such as video conferencing where the overall delay is around 100 ms. Coding is performed on a 4:2:0 video signals. The main profile adds support for B-pictures and is the most widely used profile. Using B-pictures increases the picture quality, but adds about 120 ms to the coding delay to allow for the picture reordering. Main profile decoders will also decode MPEG-1 video. Currently, most MPEG-2 video decoder chip-sets support the main profile at main level. ISSN : 0976-5166 242 S. Vetrivel et. al. / Indian Journal of Computer Science and Engineering Vol. 1 No. 4 240-250 C. Details of scalable profiles: The SNR profile adds support for enhancement layers of DCT coefficient refinement, using the 'signal to noise (SNR) ratio scalability' tool. The SNR profile is suggested for digital terrestrial television as a way of providing graceful degradation. The spatial profile adds support for enhancement layers carrying the coded image at different resolutions, using the 'spatial scalability' tool. Spatial scalability is characterised by the use of decoded pictures from a lower layer as a prediction in a higher layer. If the higher layer is carrying the image at a higher resolution, then the decoded pictures from the lower layer must be sample rate converted to the higher resolution by means of an 'up-converter'. The spatial profile is suggested as a way to broadcast a high-definition TV service with a main-profile compatible standard-definition service. In MPEG-2 Transcoding differs from first generation coding, in that a transcoder only has access to a previously compressed signal which already contains quantisation noise compared to the original source signal. [2] IV. MPEG-4 (1998) This is based on the foundation of MPEG-1 and 2 as can be seen in Figure 2.The DCT transform is used along with similar quantization tables and entropy coders. The advances are with the use of multiple VLC tables and half pixel fractional motion estimation accuracy. In the area of Audio, new tools are added in MPEG-4 Version 2 to provide the following new functionalities: [11]  Error Resilience tools provide improved performance on error-prone transmission channels.  _Low-Delay Audio Coding tools support the transmission of general audio signals in applications requiring low coding delay, such as real-time bi-directional communication.  _Small Step Scalability tools provide scalable coding with very fine granularity, i.e. embedded coding with very small bitrate steps, based on the General Audio Coding tools of Version 1.  _Parametric Audio Coding tools combine very low bitrate coding of general audio signals with the possibility of modifying the playback speed or pitch during decoding without the need for an effects processing unit.  _Environmental Spatialisation tools enable composition of an “audio scene” with more natural sound source and sound environment modeling than is possible in Version 1. MPEG-4 is an object oriented based image codec and actually uses the wavelet transform to represent textural information [8]. The steps involved in decompression are shown in figure and it should be noted that one of the aims of having a low complexity decoded has been met. MPEG-4 principally offers four error resilience tools. Figure 4. MPEG-4 Video Coder Basic Block Diagram ISSN : 0976-5166 243 S. Vetrivel et. al. / Indian Journal of Computer Science and Engineering Vol. 1 No. 4 240-250 A. Application MPEG-4 aimed at multimedia applications including streaming video applications on mobile devices [6]. IV. MPEG-7 MPEG-7 is a multimedia content description standard. It was standardized in ISO/IEC 15938 (Multimedia content description interface). This description will be associated with the content itself, to allow fast and efficient searching for material that is of interest to the user. MPEG-7 is formally called Multimedia Content Description Interface. The ultimate goal and objective of MPEG-7 is to provide interoperability among systems and applications used in generation, management, distribution, and consumption of audio-visual content descriptions. [3] It uses XML to store metadata, and can be attached to timecode in order to tag particular events, or synchronise lyrics to a song, for example. It was designed to standardize:  a set of Description Schemes (short DS in the standard) and Descriptors (short D in the standard)  a language to specify these schemes, called the Description Definition Language (short DDL in the standard)  a scheme for coding the description The combination of MPEG-4 and MPEG-7 has been sometimes referred to as MPEG-47.