MPEG-2
MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth.
MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. It also specifies the format of movies and other programs that are distributed on DVD and similar discs. As such, TV stations, TV receivers, DVD players, and other equipment are often designed to this standard. MPEG-2 was the second of several standards developed by the Moving Pictures Expert Group (MPEG) and is an international standard (ISO/IEC 13818). Parts 1 and 2 of MPEG-2 were developed in a joint collaborative team with ITU-T, and they have a respective catalog number in the ITU-T Recommendation Series.
While MPEG-2 is the core of most digital television and DVD formats, it does not completely specify them. Regional institutions can adapt it to their needs by restricting and augmenting aspects of the standard. See Profiles and Levels.
MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. One is the Transport Stream, designed to carry digital video and audio over possibly lossy media, such as broadcasting, examples of which include ATSC, DVB and SBTVD. MPEG-2 Systems also defines Program Stream, a container format designed for reasonably reliable media such as optical discs, DVDs and SVCDs. MPEG-2/System is formally known as ISO/IEC 13818-1 and as ITU-T Rec. H.222.0.
The Video section, part 2 of MPEG-2, is similar to the previous MPEG-1 standard, but also provides support for interlaced video, the format used by analog broadcast TV systems. MPEG-2 video is not optimized for low bit-rates, especially less than 1 Mbit/s at standard definition resolutions. However, it outperforms MPEG-1 at 3 Mbit/s and above. All standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams. MPEG-2/Video is formally known as ISO/IEC 13818-2 and as ITU-T Rec. H.262.
With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems.
The MPEG-2 Audio section, defined in part 3 of the standard, enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels. This method is backwards-compatible, allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.
Part 7 of the MPEG-2 standard specifies a rather different, non-backwards-compatible audio format. Part 7 is referred to as MPEG-2 AAC. AAC is more efficient than the previous MPEG audio standards, and is in some ways less complicated than the its predecessor, MPEG-1 Audio, Layer 3, in that it does not have the hybrid filter bank. Advanced Audio is also defined in Part 3 of the MPEG-4 standard.
MPEG-2 evolved out of the shortcomings of MPEG-1.
MPEG-1's known weaknesses:
- a less efficient audio compression system
- lack of flexibility (fewer variations of acceptable packet types)
- does not support interlaced footage