What is MPEG-2?

MPEG-2 (H.222/H.262 as defined by the ITU) is a standard for the generic coding of moving pictures and associated audio information and metadata such as subtitles and closed captioning. 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 for uses such as reference, archiving filmed material, editing and transcription. 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. 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).

MPEG-2 relates to how video is delivered but not how it is encoded. So whether a video is transport stream or program stream has nothing to do with the quality of the video encoding or the MPEG-2 GOP structure. The format for delivery is independent of the content. The different formats exist because there are conflicting applications. Someone saving MPEG-2 to a file on a computer is not concerned about transmission, whereas someone wanting to transmit MPEG-2 would be very concerned with file format. The MPEG-2 standards address both of these concerns.

MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. One is the transport stream, a data packet format designed to transmit one data packet in four ATM data packets for streaming digital video and audio over fixed or mobile transmission mediums, where the beginning and the end of the stream may not be identified, such as radio frequency, cable and linear recording mediums, examples of which include ATSC, DVB, ISDB and SBTVD broadcasting, and HDV recording on tape. The other is the program stream, an extended version of the MPEG-1 container format without the extra overhead of transport stream designed for random access storage mediums such as hard disk drives, optical discs and flash memory. An MPEG-2 program stream contains only one content channel. An MPEG-2 transport stream can contain one or more content channels.

MPEG-2 is not as efficient as newer standards such as H.264 and Opus. However, its backwards compatibility with existing hardware and software means it is still widely used, for example, in the DVD-Video standard. Some of the filename extensions related to MPEG-2 audio and video file formats are .mpg, .mpeg, .m2v, .mp2, mp3.