MPEG2 Vs. MPEG4

MPEG2 and MPEG4 are widely used audio/video compression standards in many multimedia applications, ranging from mobile devices to DVD players. This article points out the prime differences between these standards, with regards to compression, quality and applications.

The rise of the Internet as an entertainment medium, DVD players, availability of satellite-based DTH cable services and the development of mobile devices prompted a parallel evolution of video and audio compression formats, that could be easily streamed through these new mediums. MPEG (Moving Picture Experts Group) is a cluster of audio/video standards developed for the sole purpose of providing superior compression, digital encoding and decoding techniques, that achieve the optimum usage of resources, without compromising quality. MPEG-2 and MPEG-4 are parts of the entire MPEG definition, describing various compression and transmission standards for audio and visual information on different mediums. Both these standards were released in sections, with improvements made and new features added at every stage.

MPEG2 Vs. MPEG4 Comparison
MPEG2 and MPEG4 are bunched coding technologies, used to compress audio and video data files, to facilitate their maximally optimized transmission and usage. These coding techniques are a collection of patented data compression programs, aimed at converting the audio/video data, in such a form, that its memory size and transmission is optimized, within the constraints of the transmission medium, while providing superior picture and audio quality.

Introduction
Index

• Compression
• File Size
• Quality
• Bit Rate
• Bandwidth

MPEG-2, developed in 1995, was primarily devoted to creation of efficient transmission, compression and coding technologies for television broadcast. With support for high-definition picture quality and interlaced, as well as progressive scanning, this set of coding formats is used in digital TV broadcast, over-the-air digital television (ISDB, DVB, ATSC), DVD (Video), VCD and even Blu-ray Discs. It uses lossy compression techniques for audio and video files, to reduce file sizes substantially.

MPEG-4, created in 1998, was primarily conceptualized with the objective of achieving higher compression, compared to the earlier MPEG-2 format, while enhancing audio and visual output quality. In short, better picture or audio quality through lesser file size, was the goal. It was specifically developed for applications that require optimization in file size, due to transmission media limitations.

This includes video and audio streaming on the Internet, telephony services, DTH satellite television and storage media like Blu-ray. Most modern video codecs are based on MPEG-4. It wouldn’t be an understatement to say that MPEG-4 is displacing MPEG-2 in most domains because of its versatility. Not only does MPEG-4 achieve high compression, but it also provides superior picture quality. The standard has received greater acceptance in recent times, due to the proliferation of mobile devices where it finds the greatest application.

MPEG-4 is a vast collection of compression formats, divided in ten parts, with each finding different applications. The ones that find wide application are MPEG-4 Part 2 (used by codecs like Xvid, Nero Digital and DivX) and H.264/MPEG-4 Part 10 (the codec used by web video streaming sites like Vimeo and YouTube, iTunes Store and Blu-ray discs). Other parts include compression techniques for 3D graphics, web video coding, audio, ISO base media file formats (like 3GP) and streaming text formats.

Compression
Video or audio compression is all about maintaining the same audio or video quality in lesser number of bits. MPEG-4 compression is an improvement over MPEG-2 format in that respect.

How did MPEG-2 format achieve file size compression without quality loss? This was done by removing certain redundant parts from a frame which are repeated in the later ones. This process is known as lossy compression. Parts of the picture frame that remain static are stored only once. Only the differences between successive frames will be stored later. The bit rate is also controlled accordingly. There are many other mathematical tricks involved which reduce file size while encoding. This way, the video file is encoded in MPEG-2 format and size is substantially reduced. So when you play such a file, your video player must have the MPEG-2 decoder to render back original frames from compressed form.

MPEG-4 compression is quite complicated compared to MPEG-2, as it is designed to create high quality videos for multimedia applications at a relatively low bit rate. To put it simply, MPEG-4 compression removes redundant bits by comparing many more frames at a time, compared to MPEG-2, by adjusting the bit rate accordingly. Compared to MPEG-2, MPEG-4 is a far more versatile encoding format. Techniques like discrete cosine transform, vector quantization and wavelet compression are used to reduce the data size of the source signal file by chiseling out temporal and spatial redundancy while retaining the essentials. Mathematical transforms and algorithms based on information theory are extensively used for the purpose.
File Size
Compared to MPEG-2 files, MPEG-4 files take up less memory size. This is because of the superior compression algorithm used in MPEG-4, which lets video and audio files to be transported over the Internet and streamed on multiple network platforms.
Quality
MPEG-2 is the industry standard and the videos you watch on DVD and digital television are encoded in it. The quality of MPEG-2 is impeccable, but this format is not made for multimedia network applications. It is not made for streaming videos on the phone or for broadcast applications. The large file sizes it generates, make it an impractical choice for online streaming.

On the other hand, parts of MPEG-4 are exclusively developed for multimedia streaming applications on the Internet. So a video encoded in it, will provide a better quality video or audio when streamed online. With MPEG-4 format, video conferencing is possible. MPEG-4 surpasses MPEG-2 in picture and audio quality overall.
Bit Rate
Files encoded in MPEG-2 format have a bit rate ranging from 4 to 80 MB per second, while MPEG-4 files have a bit rate which is comparatively low (ranging from a few kilobytes to megabytes per second). This is because the format is designed for a range of applications.

Bandwidth
If you compare MPEG-2 and MPEG-4, with respect to bandwidth, you will find a substantial difference. This can be easily demonstrated by encoding and comparing files in the two formats and checking their size, as well as bandwidth. Usually, MPEG-4 has less than half the bandwidth of an MPEG-2 signal, which makes it ideal for streaming. It is true that MPEG-4 encoding is computationally more demanding compared to other formats, but the end result justifies the time invested.
Both formats are in use today for different applications. MPEG-2 is still used in DVD encoding and TV broadcast while the Internet and video encoding in general is the domain of MPEG-4, as it keeps evolving to serve newer demands.