Tuesday, October 09, 2007

MPEG Standards

Whenever we're listening to music on the ipod or playing an audio cd or watching a movie on DVD we are making use of MPEG standards. The Motion Picture Experts Group or MPEG is responsible for the development of standards for Audio/Video Playback & Compression ( encoding ) . There are four such standards that MPEG has released so far namely MPEG1 , MPEG2 , MPEG4 and MPEG7.

MPEG1 (1992) ; Supports both Video and Audio, Video bitrates upto 1.5Mbps , 2 Channel Audio ( Stereo / Mono ) with sample rates 32,44,48 kHz.

MPEG2 (1994); Supports higher sampling rates up to 96khz and low bitrates , multi channel audio ( 5.1 surround sound , 5 audio channels and one channel for the woofer ). DVD’S , AAC ( Advanced Audio Coding ) are based on this standard.

MPEG Layers are supported by both MPEG2 and MPEG1 , each layer supports the features of the layers below. Higher layer provides better quality at higher bitrates.

MPEG Layer 1 ; relatively old standard designed for Digital Compact Discs.

MPEG Layer 2 or MP2 widely used within the broadcasting industry , offers high quality audio at higher bitrates.

MPEG Layer 3 or MP3 , decent ( not so bad ) audio quality at lower bitrates, this format has improved over the years. VBR and CBR are two such ways to handle bitrates improving the performance of the resulting audio.

MPEG4 (1998) ; This standard goes beyond the earlier two standards, it makes use of both MPEG1, MPEG2 standards and while adding a lot of newer features. MPEG4 is more of a audio/video encoding standard aimed for the future; providing support for a wide range of video/audio applications ( i.e web streaming , videophones , digital broadcasting ) with different bandwidth & performance requirements.

This standard is divided into parts , most notable being the

MPEG-4 Part 2 used by codecs like divX , Xvid , Quicktime 6

MPEG-4 Part 10 for next gen formats like HD-DVD and blu-ray

This standard is continuously improving

MPEG7 (2001) ; also called Multimedia Content Description Interface provides framework for managing audio data supported by past standards.

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