Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
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Format Description Categories >> Browse Alphabetical List
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Table of Contents
• Identification and description • Local use • Sustainability factors • Quality and functionality factors • File type signifiers • Notes • Format specifications • Useful references
Format Description Properties
• ID: fdd000028 • Short name: MPEG-2 • Content categories: moving image • Format category: bitstream encoding, file format • Last significant update: 2006-11-29 • Draft status: Full Identification and description
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| Full name | ISO/IEC 13818. Information technology -- Generic coding of moving pictures and associated audio information (formal name) MPEG-2 (common name) |
| Description | Encoding for compressed video and audio data multiplexed with signaling information in a serial bistream. The format was initially developed to serve the transmission of compressed television programs via broadcast, cablecast, and satellite, and subsequently adopted for DVD production and for some online delivery systems. The term stream is used to name the format's sequence of encoded bytes. Elementary streams contain video, audio, or other data; a video elementary stream contains compressed video frames, plus sequence headers, group-of-picture (GOP) headers, and other data needed to decode the stream. An elementary stream is broken up into packets of variable length, forming a packetized elementary stream (PES). Each PES packet includes a header. In many applications, the audio and video are multiplexed, thus combining the two elements. Packetized and multiplexed elementary streams may take the form of single-program program streams or be incorporated with other programs in a multi-program transport stream. |
| Production phase | Generally a final-state (end-user delivery) format; MPEG-2_MP, Main Profile, or MPEG-2_422, 4:2:2 Profile, may be used as middle-state (broadcast production) formats. |
| Relationship to other formats | |
| Other | Identical to the ITU-T standard H.262 |
| Supertype of | MPEG-2_SP, Simple Profile |
| Supertype of | MPEG-2_MP, Main Profile |
| Supertype of | MPEG-2_422, 4:2:2 Profile |
| Supertype of | Other MPEG-2 profiles not documented at this time: SNR Scalable, Spatially Scalable, and High. |
| Supertype of | MP3_ENC MP3 audio encoding |
| Supertype of | AAC_MP2 Advanced Audio Coding (MPEG-2) |
| LC experience or existing holdings | MPEG-2 (specific profile unknown) used as the best digital computer-file format for video recordings reformatted by the American Folklife Center Save Our Sounds and Veterans History projects. In these projects, the best copy from an archival perspective is the source videotape (digital Betacam). All experience based on the reproduction of NTSC or standard definition ATSC signals. |
| LC preference | For file-based compressed video, conform to or approximate MPEG-2_422 (4:2:2 Profile) at Main Level (aka MPEG-2 422@ML) or MPEG-2_MP (Main Profile) at Main Level (aka MPEG-2 MP@ML). Uncompressed or losslessly compressed copies are preferred to compressed (for future development). |
| Disclosure | Open standard. Developed by ISO technical program JTC 1/SC 29 (WG11), aka the Motion Pictures Expert Group (MPEG), Coding of audio, picture, multimedia and hypermedia information. Developed in joint partnership with ITU-T, who published the "common text" as H. 262. |
| Documentation | ISO/IEC 13818; first approvals in 1994. Ten parts have been published; parts 1, 2, 3, and 7 are central. Part 2 concerns the coding and specifies profiles and levels. See list of ISO documents in Format specifications below. |
| Adoption | Widely adopted for filemaking, DVD disks, and other applications.
Most significant is the format's required use in digital terrestrial
broadcasting to homes in the United States and several other
nations, as governed by the ATSC (Advanced Television Systems Committee)
specifications. Many software tools exist for encoding and decoding. MPEG-1 and MPEG-2 are recommended data formats in the list of FCLA recommended formats (Florida Center for Library Automation; www.fcla.edu/digitalArchive/pdfs/recFormats.pdf), although no profiles or levels are specified. Wide adoption may not extend to all profiles, levels, or parts of the standard. [Evidence in various documents suggests that the Simple, Main, and 4:2:2 profiles are the most widely adopted. Comments welcome] |
| Licensing and patent claims | Managed by MPEG LA LLC (http://www.mpegla.com/). Licenses pertain to tools and not to streams or files per se. |
| Transparency | Depends upon algorithms and tools to read; will require sophistication to build tools. |
| Self-documentation | Technical (coding) information is contained in the MPEG-2 bitstream in macroblock headers, slice headers, picture headers, Group of Picture (GOP) headers, and sequence headers. The sequence header provides data needed before decoding can begin, such as the size of the picture and the frame rate. Because it is so important, the sequence header is usually repeated as often as twice a second. The lack of metadata of the type called bibliographic by librarians motivated the MPEG group to develop MPEG-7, a separately standardized structure for metadata to support discovery and other purposes. |
| External dependencies | Playback of surround sound requires multiple loudspeakers. |
| Technical protection considerations | None |
| Video elements | |
| Normal rendering for video | Good support. |
| Clarity (support for high video image resolution) | Moderate to very good, given that this is a format for compression. Outcome will depend on the type and extent of compression, and the encoder used. |
| Functionality beyond normal video rendering | The MPEG-2 transport stream permits the multiplexing of multiple programs. |
| Sound elements | |
| Normal rendering for sound | Good support. |
| Fidelity (support for high audio resolution) | Moderate to very good, given that the options for audio employ compression. Widespread use is made of MPEG-2 layer 3 audio, aka MP3_ENC. Some producers make use of Advanced Audio Coding, aka AAC, considered to be superior to MP3 at a given bit rate. Producers are not limited to the audio structures inherent in MPEG-2. The Society of Motion Picture and Television Engineers (SMPTE) provides specifications for incorporating AES3_SMPTE data into the MPEG-2 transport stream. Among other things, this permits the use of AC-3 compressed audio (aka Dolby Digital). For all types of compressed audio, the quality of the outcome will depend on the type and extent of compression, and the encoder used. |
| Support for multiple sound channels | Multi-channel sound is supported in both the backwardly compatible (BC) audio structures shared with MPEG-1, which includes layer 3 audio (MP3_ENC), and in the non-backwardly compatible AAC audio structure. MPEG-2 BC can deliver five main channels and an optional LFE (Low Frequency Encoding or Effects) channel, i.e., 5.1 surround sound. AAC provides a capability of up to 48 main audio channels, 16 LFE channels, 16 overdub/multilingual channels, and 16 data streams. The use of AC-3 compressed audio (aka Dolby Digital), described above in connection with AES3_SMPTE data, provides another means for presenting surround sound. |
| Functionality beyond normal sound rendering | None |
| Tag type | Value | Note |
| Filename Extension | mpg, mpeg | There is no explicit MPEG-2 file format; MPEG-2 content "ready to be delivered" is exchanged in a de facto file format that may carry one of these extensions. |
| Filename Extension | mod | Reported to be used by the Panasonic SV-AV100 camcorder (from Shopping.com, as documented April 13, 2006) |
| Internet Media Type | video/mpeg | From IETF (Internet Engineering Task Force) RFC 2046 |
| Internet Media Type | video/mpv video/mp2t video/mp1s video/mp2p | From IETF (Internet Engineering Task Force) RFC 3555; the four subtypes are glossed as "MPEG-1 or -2 Elementary Streams," "MPEG-2 Transport Streams," "MPEG-1 Systems Streams," and "MPEG-2 Program Streams." |
| Internet Media Type | video/mpg video/x-mpg video/mpeg2 application/x-pn-mpg video/x-mpeg video/x-mpeg2a | Additional examples selected from The File Extension Source. |
| Magic numbers | Hex: 00 00 01 Bx ASCII: .... | From Gary Kessler's File Signatures Table. |
| General | VOB (DVD Video OBject) files are closely related to MPEG-2 files. VOB files are assembled by DVD producers, and they contain the actual Video, Audio, Subtitle, and Menu contents in stream form. The Wikipedia entry for VOB (as of November 28, 2006), reports that "VOB files are encoded very much like standard MPEG-2 files. When the extension is renamed from .vob to .mpg or .mpeg the file will still be readable and will continue to hold all information, although most players supporting MPEG-2 don't support subtitle tracks. In order to burn the VOB files to a DVD±R disc, other standard DVD-Video files are needed as well, including IFO and BUP files." From zatznotfunny: "TiVoToGo files, having the .tivo extension, are essentially encrypted and fingerprinted mpeg [MPEG-2] files. MPEG is a common video format. Your unique Media Access Key (MAK) is appended to all shows as text, and perhaps embedded as a watermark in other ways. The TiVo Desktop software includes a .dll that is used to decrypt, or unlock, your show using your MAK. TiVo files can be viewed, converted, edited, transferred, and/or burned." |
| History | MPEG stands for the Motion Pictures Expert Group, which began developing video compression standards in the 1980s. The group was founded by two men described by one commentator as "the fiery Leonardo Chiariglione (CSELT, Italy)" and "the peaceful Hiroshi Yasuda (JVC, Japan)." MPEG's initial development (of MPEG-1) was partly inspired by the H.261 video coding standard published by the ITU (International Telecom Union). |
URLs
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• ISO/IEC 13818-1:2000 Information technology -- Generic coding of moving pictures and associated audio information: Systems. Two primary purposes: 1). a syntax for transporting packets of audio and video bitstreams over digital channels and storage media, 2). a syntax for synchronizing video and audio streams.1
• ISO/IEC 13818-1:2000/Cor 1:2002
• ISO/IEC 13818-1:2000/Cor 2:2002
• ISO/IEC 13818-1:2000/Amd 1:2003 Carriage of metadata over ISO/IEC 13818-1 streams
• ISO/IEC 13818-1:2000/Amd 2:2004 Support of IPMP on MPEG-2 systems
• ISO/IEC 13818-2:2000 Information technology -- Generic coding of moving pictures and associated audio information: Video. Jointly developed with the ITU-T, where it is known as recommendation H.262. Describes syntax (header and bitstream elements) and semantics (algorithms telling what to do with the bits).
• ISO/IEC 13818-2:2000/Cor 1:2002
• ISO/IEC 13818-2:2000/Amd 1:2001 Content description data
• ISO/IEC 13818-3:1998 Information technology -- Generic coding of moving pictures and
associated audio information -- Part 3: Audio. Describes syntax and semantics for three classes of compression methods. Known as Layers I, II, and III, the classes trade increased syntax and coding complexity for improved coding efficiency at lower bitrates.
• ISO/IEC 13818-4:1998 Information technology -- Generic coding of moving pictures and associated audio information -- Part 4: Conformance testing. Conformance testing. Defines the meaning of MPEG conformance for all three parts (Systems, Video, and Audio), and provides two sets of test guidelines for determining compliance in bitstreams and decoders.
• ISO/IEC 13818-4:1998/Amd 1:1999/Cor 1:2003
• ISO/IEC 13818-4:1998/Amd 3:2000/Cor 1:2003
• ISO/IEC 13818-4:1998/Cor 2:1998
• ISO/IEC 13818-4:1998/Amd 1:1999 Advanced Audio Coding (AAC) conformance testing
• ISO/IEC 13818-4:1998/Amd 2:2000 System target decoder model
• ISO/IEC 13818-4:1998/Amd 3:2000 Additional audio conformance bitstreams
• ISO/IEC TR 13818-5:1997 Information technology -- Generic coding of moving pictures and associated audio information -- Part 5: Software simulation. Contains an example ANSI C language software encoder and compliant decoder for video and audio.
• ISO/IEC TR 13818-5:1997/Amd 1:1999/Cor 1:2003
• ISO/IEC TR 13818-5:1997/Amd 1:1999 Advanced Audio Coding (AAC)
• ISO/IEC 13818-6:1998 Information technology -- Generic coding of moving pictures and associated audio information -- Part 6: Extensions for DSM-CC. Extensions for Digital Storage Medium Command and Control (DSM-CC). Provides a syntax for controlling VCR-style playback and random-access of bitstreams encoded onto digital storage mediums such as compact disc.
• ISO/IEC 13818-6:1998/Amd 1:2000/Cor 1:2002
• ISO/IEC 13818-6:1998/Cor 1:1999
• ISO/IEC 13818-6:1998/Cor 2:2002
• ISO/IEC 13818-6:1998/Amd 1:2000 Additions to support data broadcasting
• ISO/IEC 13818-6:1998/Amd 2:2000 Additions to support synchronized download services, opportunistic data services and resource announcement in broadcast and interactive services
• ISO/IEC 13818-6:1998/Amd 3:2001 Transport buffer model in support of synchronized user-to-network download protocol
• ISO/IEC 13818-7:2003 Information technology -- Generic coding of moving pictures and associated audio information -- Part 7: Advanced Audio Coding (AAC). Standard for higher-quality multichannel audio than achievable using MPEG-1 backwards-compatible audio.
• ISO/IEC 13818-7:2003/Amd 1:2004 Embedding of bandwidth extension
• Part 8. 10-bit video extension. Withdrawn.
• ISO/IEC 13818-9:1996 Information technology -- Generic coding of moving pictures and associated audio information -- Part 9: Extension for real time interface for systems decoders. Real-Time Interface (RTI) for systems decoders defines a syntax for video on demand control signals between set-top boxes and head-end servers.
• ISO/IEC 13818-10:1999 Information technology -- Generic coding of moving pictures and associated audio information -- Part 10: Conformance extensions for Digital Storage Media Command and Control (DSM-CC). Related to part 6.
• ISO/IEC 13818-11:2004 Information technology -- Generic coding of moving pictures and associated audio information -- Part 11: IPMP on MPEG-2 systems
1 The italicized blurbs in the specifications section are derived from the Berkeley Multimedia Research Center MPEG-2 FAQ (http://bmrc.berkeley.edu/frame/research/mpeg/mpeg2faq.html).
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