MPEG-2 is used in Digital Video Broadcast and Digital Versatile Discs. The MPEG transport stream, TS, and MPEG program stream, PS, are container formats.

MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information".^[1] 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.

Main characteristics[link]

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). 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[link]

MPEG-2 includes a Systems section, part 1, that defines two distinct, but related, container formats. One is the MPEG transport stream, designed to carry digital video and audio over possibly lossy media, where the beginning and the end of the stream may not be identified, such as broadcasting or magnetic tape, examples of which include ATSC/DVB/ISDB/SBTVD broadcasting, and HDV recording on tape. MPEG-2 Systems also defines the MPEG program stream, a container format designed for file-based media such as hard disk drives, optical discs and flash memory.

MPEG-2 Systems is formally known as ISO/IEC 13818-1 and as ITU-T Rec. H.222.0.^[2][3] 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 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.^[4]

Video[link]

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. All standards-compliant MPEG-2 Video decoders are fully capable of playing back MPEG-1 Video streams conforming to the Constrained Parameters Bitstream syntax. MPEG-2/Video is formally known as ISO/IEC 13818-2 and as ITU-T Rec. H.262.^[5]

With some enhancements, MPEG-2 Video and Systems are also used in some HDTV transmission systems.

Audio[link]

MPEG-2 introduces new audio encoding methods compared to MPEG-1:^[6]

MPEG-2 Part 3[link]

The MPEG-2 Audio section, defined in Part 3 (ISO/IEC 13818-3) of the standard, 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 (also known as MPEG-2 BC^{[7][8][9][10]}), allowing MPEG-1 audio decoders to decode the two main stereo components of the presentation.^[11] MPEG-2 part 3 also defined additional bit rates and sample rates for MPEG-1 Audio Layer I, II and III.^[12]

MPEG-2 BC (backward compatible with MPEG-1 audio formats)^[7][8][11]

• low bitrate encoding with halved sampling rate (MPEG-1 Layer 1/2/3 LSF - a.k.a. MPEG-2 LSF - "Low Sampling Frequencies")
• multichannel encoding with up to 5.1 channels, a.k.a. MPEG Multichannel

MPEG-2 Part 7[link]

Part 7 (ISO/IEC 13818-7) of the MPEG-2 standard specifies a rather different, non-backwards-compatible audio format^[9] (also known as MPEG-2 NBC^[7][8][13]). 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 its predecessor, MPEG-1 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.^[6] Advanced Audio is also defined in Part 3 of the MPEG-4 standard.

MPEG-2 NBC (Non-Backward Compatible)^[7][8]

• MPEG-2 AAC
• multichannel encoding with up to 48 channels

ISO/IEC 13818[link]

MPEG-2 standards were published as parts of ISO/IEC 13818. Each part covers a certain aspect of the whole specification.

Part 1

Systems – describes synchronization and multiplexing of video and audio. (It is also known as ITU-T Rec. H.222.0.^[2]) See MPEG transport stream and MPEG program stream.

Part 2

Video – compression codec for interlaced and non-interlaced video signals (Also known as ITU-T Rec. H.262).

Part 3

Audio – compression codec 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 of MPEG-1 audio.

Part 4

Describes procedures for testing compliance.

Part 5

Describes systems for Software simulation.

Part 6

Describes extensions for DSM-CC (Digital Storage Media Command and Control).

Part 7

Advanced Audio Coding (AAC).

Part 9

Extension for real time interfaces.

Part 10

Conformance extensions for DSM-CC.

Part 11

Intellectual property management (IPMP)

(Part 8: 10-bit video extension. Primary application was studio video. Part 8 has been withdrawn due to lack of interest by industry.)

History[link]

MPEG-2 evolved out of the shortcomings of MPEG-1.

MPEG-1's known weaknesses:

• an audio compression system limited to two channels (stereo.)
• 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 color space, 4:2:0.

This section requires expansion.

Filename extensions[link]

.mpg, .mpeg, .m2v, .mp2, mp3 are some of a number of filename extensions used for MPEG-1 or MPEG-2 audio and video file formats.

Applications[link]

DVD-Video[link]

The DVD-Video standard uses MPEG-2 video, but imposes some restrictions:

• Allowed Dimensions
  • 720 × 480, 704 × 480, 352 × 480, 352 × 240 pixel (NTSC)
  • 720 × 576, 704 × 576, 352 × 576, 352 × 288 pixel (PAL)
• Allowed Aspect ratios (Display AR)
  • 4:3
  • 16:9 (1.85:1 and 2.35:1, among others, are often listed as valid DVD aspect ratios, but are actually a "letterboxed" 16:9 image)
• Allowed Frame rates
  • 29.97 frame/s (NTSC)
  • 25 frame/s (PAL)

Note: By using a pattern of REPEAT_FIRST_FIELD flags on the headers of encoded pictures, pictures can be displayed for either two or three fields and almost any picture display rate (minimum ⅔ of the frame rate) can be achieved. This is most often used to display 23.976 (approximately film rate) video on NTSC.

• 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 (NTSC only)
• Audio
  • Linear Pulse Code Modulation (LPCM): 48 kHz or 96 kHz; 16- or 24-bit; up to six channels (not all combinations possible due to bitrate constraints)
  • MPEG Layer 2 (MP2): 48 kHz, up to 5.1 channels (required in PAL players only)
  • Dolby Digital (DD, also known as AC-3): 48 kHz, 32–448 kbit/s, up to 5.1 channels
  • Digital Theater Systems (DTS): 754 kbit/s or 1510 kbit/s (not required for DVD player compliance)
  • 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 (Group Of Pictures)
  • Sequence header must be present at the beginning of every GOP
  • Maximum frames per GOP: 18 (NTSC) / 15 (PAL), i.e. 0.6 seconds both
  • Closed GOP required for multi-angle DVDs

HDV[link]

HDV is a format for recording and playback of high-definition MPEG-2 video on a DV cassette tape.

MOD and TOD[link]

MOD and TOD are recording formats for use in consumer digital file-based camcorders.

XDCAM[link]

XDCAM is a professional file-based video recording format.

DVB[link]

Application-specific restrictions on MPEG-2 video in the DVB standard:

Allowed resolutions for SDTV:

• 720, 640, 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, 704, 544, 528, 480 or 352 × 576 pixel, 25 frame/s
• 352 × 288 pixel, 25 frame/s

For HDTV:

• 720 x 576 x 50 frame/s progressive (576p50)
• 1280 x 720 x 25 or 50 frame/s progressive (720p50)
• 1440 or 1920 x 1080 x 25 frame/s progressive (1080p25 = film mode)
• 1440 or 1920 x 1080 x 25 frame/s interlace (1080i50)

ATSC[link]

The ATSC A/53 standard used in the United States, uses MPEG-2 video at the Main Profile @ High Level, with additional restrictions such as the maximum bitrate of 19.4 Mbit/s for broadcast television and 38.8 Mbit/s for cable television, 4:2:0 chroma subsampling format, and mandatory colorimetry information.

ATSC allows the following video resolutions, aspect ratios, and frame/field rates:

• 1920 × 1080 pixel (16:9, square pixels), at 30p, 29.97p, 24p, 23.976p, 60i, 59.94i.
• 1280 × 720 pixel (16:9, square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, or 23.976p
• 704 × 480 pixel (4:3 or 16:9, non-square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i
• 640 × 480 pixel (4:3, square pixels), at 60p, 59.94p, 30p, 29.97p, 24p, 23.976p, 60i, or 59.94i

ATSC standard A/63 defines additional resolutions and aspect rates for 50 Hz (PAL) signal.

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 (news, soap operas) and 24 Hz progressive (prime-time) content without ending the MPEG-2 sequence and introducing a 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 codec 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[link]

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.

Patent holders[link]

MPEG Licensing Authority, a private patent licensing organization, has acquired rights from over 20 corporations and one university to license a patent pool of approximately 640 worldwide patents, which it claims are the "essential" to use of MPEG-2 technology, although many of the patents have since expired.^[33][34] Where software patentability is upheld, the use of MPEG-2 requires the payment of licensing fees to the patent holders. Other patents are licensed by Audio MPEG, Inc.^[35] The development of the standard itself took less time than the patent negotiations.^[36][37] Patent pooling between essential and peripheral patent holders in the MPEG-2 pool is the subject of a study by the University of Wisconsin.^[38]

MPEG-2 patents (U.S. only)[link]

According to the MPEG-LA Licensing Agreement MPEG-LA, any use of MPEG-2 technology is subject to royalties.

• Encoders are subject to a royalty of $2.00 per unit.
• Decoders are subject to a royalty of $2.00 per unit.^[39]
• Royalty-based sales of encoders and decoders are subject to different rules and $2.50 per unit.^[39]
• Also, any packaged medium (DVDs/Data Streams) is subject to licence fees according to length of recording/broadcast.

In the case of free software such as VLC media player (which uses the ffmpeg library) and in which the software is not sold, the end-user bears the royalty.^{[citation needed]}

See also[link]

• MPEG encoding
• MPEG-1 Audio Layer II (MP2)
• MPEG-1 Audio Layer III (MP3)
• DVD
• DVB-S2

References[link]

External links[link]

• A Beginners Guide for MPEG-2 Standard
• MPEG-2 Overview (figures are lost)
• MPEG-2 video compression
• MIT 6.344 – Slides from lectures on video compression at MIT.
• A Discrete Cosine Transform tutorial
• IPTV MPEG and Quality of Experience Testing
• OpenIPMP: Open Source DRM Project for MPEG-2
• ISO/IEC 13818 – MPEG-2 at the ISO Store.
• MPEG Books - A list of MPEG reference books.