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. While MPEG-2 is not as efficient as newer standards such as H.264/AVC and H.265/HEVC, backwards compatibility with existing hardware and software means it is still widely used, for example in over-the-air digital television broadcasting and in the DVD-Video standard.
Main characteristics
MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial, 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 and is an international standard. Parts 1 and 2 of MPEG-2 were developed in a collaboration 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 Video profiles and levels.
Systems
MPEG-2 Part 1, titled Systems, 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/SBTVD broadcasting, and HDV recording on tape. The other is the program stream, an extended version of the MPEG-1 container format with less overhead than transport stream. Program stream is designed for random access storage mediums such as hard disk drives, optical discs and flash memory.Transport stream file formats include M2TS, which is used on Blu-ray discs, AVCHD on re-writable DVDs and HDV on compact flash cards. Program stream files include VOB on DVDs and Enhanced VOB on the short lived HD DVD. The standard MPEG-2 transport stream contains packets of 188 bytes. M2TS prepends each packet with 4 bytes containing a 2-bit copy permission indicator and 30-bit timestamp.
ISO authorized the "SMPTE Registration Authority, LLC" as the registration authority for MPEG-2 format identifiers. The registration descriptor of MPEG-2 transport is provided by ISO/IEC 13818-1 in order to enable users of the standard to unambiguously carry data when its format is not necessarily a recognized international standard. This provision will permit the MPEG-2 transport standard to carry all types of data while providing for a method of unambiguous identification of the characteristics of the underlying private data.
Video
MPEG-2 Part 2, titled Video, is similar to the previous MPEG-1 Part 2 standard, but adds 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. All standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams conforming to the constrained parameters bitstream limits.With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems, and is the standard format for over-the-air ATSC digital television.
Audio
MPEG-2 introduces new audio encoding methods compared to MPEG-1:MPEG-2 Part 3
MPEG-2 Part 3, titled Audio, enhances MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel. This method is backwards-compatible with MPEG-1, allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation. This extension is called MPEG Multichannel or MPEG-2 BC.MPEG-2 Part 3 also defines additional bit rates and sampling rates for MPEG-1 Audio Layers I, II, and III. This extension is known as MPEG-2 LSF, since the new sampling rates are one-half multiples of the sampling rates defined in MPEG-1.
MPEG-2 Part 7
MPEG-2 Part 7, titled Advanced Audio Coding specifies a rather different, non-backwards-compatible audio format. This format is most commonly called Advanced Audio Coding, but was originally called MPEG-2 NBC.AAC is more efficient than the previous MPEG audio standards, and is in some ways less complicated than its predecessor, MPEG-1 Part 3 Audio Layer 3, in that it does not have the hybrid filter bank. It supports from 1 to 48 channels at sampling rates of 8 to 96 kHz, with multichannel, multilingual, and multiprogram capabilities.
AAC is also defined in MPEG-4 Part 3.
MPEG-2 Parts
MPEG-2 standards are published as "Parts". Each part covers a certain aspect of the whole specification.| Part | Number | First public release date | Latest public release date | Latest amendment | Identical ITU-T Rec. | Title | Description |
| Part 1 | 1996 | 2025 | Systems | Synchronization and multiplexing of video and audio. See MPEG transport stream and MPEG program stream. | |||
| Part 2 | 1996 | 2013 | Video | Video coding format for interlaced and non-interlaced video signals | |||
| Part 3 | 1995 | 1998 | Audio | Audio coding format for perceptual coding of audio signals. A multichannel-enabled extension and extension of bit rates and sample rates for MPEG-1 Audio Layer I, II and III. Backwards-compatible audio. | |||
| Part 4 | 1998 | 2004 | 2009 | Conformance testing | |||
| Part 5 | 1997 | 2005 | Software simulation | ||||
| Part 6 | 1998 | 1998 | 2001 | Extensions for DSM-CC | DSM-CC | ||
| Part 7 | 1997 | 2006 | 2007 | Advanced Audio Coding | Advanced Audio Coding. Non-backwards-compatible audio. | ||
| Part 8 | Withdrawn | 10-bit video extension. Primary application was studio video, allowing artifact-free processing without giving up compression. Work began in 1995, but was terminated in 2007 because of insufficient industry interest. | |||||
| Part 9 | 1996 | 1996 | Extension for real time interface for systems decoders | ||||
| Part 10 | 1999 | 1999 | Conformance extensions for Digital Storage Media Command and Control | ||||
| Part 11 | 2004 | 2004 | IPMP on MPEG-2 systems | Intellectual Property Management and Protection. XML IPMP messages are also defined in ISO/IEC 23001-3. |
History
MPEG-2 evolved out of the shortcomings of MPEG-1.MPEG-1's known weaknesses:
- An audio compression system limited to two channels
- No standardized support for interlaced video with poor compression when used for interlaced video
- Only one standardized "profile", constrained parameters bitstream, which was unsuited for higher resolution video. MPEG-1 could support 4K video but there was no easy way to encode video for higher resolutions, and identify hardware capable of supporting it, as the limitations of such hardware were not defined.
- Support for only one chroma subsampling, 4:2:0
Filename extensions
.mpg, .mpeg, and .m2v are some of a number of filename extensions used for MPEG-2 audio and video file formats. .mpg and particularly .mpeg are also used for MPEG-1 formats.File extension MP3 is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere.
Applications
DVD-Video
The DVD-Video standard uses MPEG-2 video, but imposes some restrictions:- Allowed Dimensions
- * 720 × 480, 704 × 480, 352 × 480, 352 × 240 pixel
- * 720 × 576, 702 × 576, 352 × 576, 352 × 288 pixel
- Allowed Aspect ratios
- * 4:3
- * 16:9
- Allowed frame rates
- * 29.97 interlaced frame/s
- * 23.976 progressive frame/s
- * 25 interlaced frame/s
- Audio + video bitrate
- * Video peak 9.8 Mbit/s
- * Total peak 10.08 Mbit/s
- * Minimum 300 kbit/s
- YUV 4:2:0
- Additional subtitles possible
- Closed captioning#DVDs and [Blu-ray Discs|Closed captioning]
- Audio
- * Linear Pulse Code Modulation : 48 kHz or 96 kHz; 16- or 24-bit; up to six channels
- * MPEG Layer 2 : 48 kHz, up to 5.1 channels
- * Dolby Digital : 48 kHz, 32-448 kbit/s, up to 5.1 channels
- * Digital Theater Systems : 754 kbit/s or 1510 kbit/s
- * NTSC DVDs must contain at least one LPCM or Dolby Digital audio track.
- * PAL DVDs must contain at least one MPEG Layer 2, LPCM, or Dolby Digital audio track.
- * Players are not required to play back audio with more than two channels, but must be able to downmix multichannel audio to two channels.
- GOP structure
- * Sequence header must be present at the beginning of every GOP
- * Maximum frames per GOP: 18 / 15, i.e. 0.6 seconds both
- * Closed GOP required for multi-angle DVDs
HDV
MOD and TOD
MOD and TOD are recording formats for use in consumer digital file-based camcorders.XDCAM
XDCAM is a professional file-based video recording format.DVB
Application-specific restrictions on MPEG-2 video in the DVB standard:Allowed resolutions for SDTV:
- 720, 704, 544, 528, 480 or 352 × 480 pixel, 24/1.001, 24, 30/1.001 or 30 frame/s
- 352 × 240 pixel, 24/1.001, 24, 30/1.001 or 30 frame/s
- 720, 702, 544, 528, 480 or 352 × 576 pixel, 25 frame/s
- 352 × 288 pixel, 25 frame/s
- 720 x 576 x 50 frame/s progressive
- 1280 x 720 x 25 or 50 frame/s progressive
- 1440 or 1920 x 1080 x 25 frame/s progressive
- 1440 or 1920 x 1080 x 25 frame/s interlace
ATSC
ATSC allows the following video resolutions, aspect ratios, and frame/field rates:
- 1920 × 1080 pixel, at 30p, 29.97p, 24p, 23.976p, 60i, 59.94i.
- 1280 × 720 pixel, at 60p, 59.94p, 30p, 29.97p, 24p, or 23.976p
- 704 × 480 pixel, at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i
- 640 × 480 pixel, at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i
The ATSC specification and MPEG-2 allow the use of progressive frames, even within an interlaced video sequence. For example, a station that transmits 1080i60 video sequence can use a coding method where those 60 fields are coded with 24 progressive frames and metadata instructs the decoder to interlace them and perform 3:2 pulldown before display. This allows broadcasters to switch between 60 Hz interlaced and 24 Hz progressive content without ending the MPEG-2 sequence and introducing several seconds of delay as the TV switches formats. This is the reason why 1080p30 and 1080p24 sequences allowed by the ATSC specification are not used in practice.
The 1080-line formats are encoded with 1920 × 1088 pixel luma matrices and 960 × 540 chroma matrices, but the last 8 lines are discarded by the MPEG-2 decoding and display process.
ATSC A/72 is the newest revision of ATSC standards for digital television, which allows the use of H.264/AVC video coding format and 1080p60 signal.
MPEG-2 audio was a contender for the ATSC standard during the DTV "Grand Alliance" shootout, but lost out to Dolby AC-3.
ISDB-T
Technical features of MPEG-2 in ATSC are also valid for ISDB-T, except that in the main TS has aggregated a second program for mobile devices compressed in MPEG-4 H.264 AVC for video and AAC-LC for audio, mainly known as 1seg.Blu-ray
MPEG-2 is one of the three supported video coding formats supported by Blu-ray Disc. Early Blu-ray releases typically used MPEG-2 video, but recent releases are almost always in H.264 or occasionally VC-1. Only MPEG-2 video is supported, Blu-ray does not support MPEG-2 audio. Additionally, the container format used on Blu-ray discs is an MPEG-2 transport stream, regardless of which audio and video codecs are used.Patent pool
As of January 3, 2024, MPEG-2 patents have expired worldwide, with the exception of only Malaysia, where the last patent is expected to expire in 2035. The last US patent expired on February 23, 2018.MPEG LA, a private patent licensing organization, had acquired rights from over 20 corporations and one university to license a patent pool of approximately 640 worldwide patents, which it claimed were "essential" to use of MPEG-2 technology. The patent holders included Sony, Mitsubishi Electric, Fujitsu, Panasonic, Scientific Atlanta, Columbia University, Philips, General Instrument, Canon, Hitachi, JVC Kenwood, LG Electronics, NTT, Samsung, Sanyo, Sharp and Toshiba. Where Software patentability is upheld and patents have not expired, the use of MPEG-2 requires the payment of licensing fees to the patent holders. Other patents were licensed by Audio MPEG, Inc. The development of the standard itself took less time than the patent negotiations. Patent pooling between essential and peripheral patent holders in the MPEG-2 pool was the subject of a study by the University of Wisconsin.
According to the MPEG-2 licensing agreement any use of MPEG-2 technology in countries with active patents is subject to royalties. MPEG-2 encoders and decoders are subject to $0.35 per unit. Also, any packaged medium is subject to licence fees according to length of recording/broadcast. The royalties were previously priced higher but were lowered at several points, most recently on January 1, 2018.
An earlier criticism of the MPEG-2 patent pool was that even though the number of patents had decreased from 1,048 to 416 by June 2013 the license fee had not decreased with the expiration rate of MPEG-2 patents.
Patent holders
The following organizations have held patents for MPEG-2, as listed at MPEG LA. See also List of United States MPEG-2 patents.| Organization | Patents |
| Sony Corporation | 311 |
| Thomson Licensing | 198 |
| Mitsubishi Electric | 119 |
| Philips | 99 |
| GE Technology Development, Inc. | 75 |
| Panasonic Corporation | 55 |
| CIF Licensing, LLC | 44 |
| JVC Kenwood | 39 |
| Samsung Electronics | 38 |
| Alcatel Lucent | 33 |
| Cisco Technology, Inc. | 13 |
| Toshiba Corporation | 9 |
| Columbia University | 9 |
| LG Electronics | 8 |
| Hitachi | 7 |
| Orange S.A. | 7 |
| Fujitsu | 6 |
| Robert Bosch GmbH | 5 |
| General Instrument | 4 |
| British Telecommunications | 3 |
| Canon Inc. | 2 |
| KDDI Corporation | 2 |
| Nippon Telegraph and Telephone | 2 |
| ARRIS Technology, Inc. | 2 |
| Sanyo Electric | 1 |
| Sharp Corporation | 1 |
| Hewlett-Packard Enterprise Company | 1 |