Sustainability of Digital Formats: Planning for Library of Congress Collections

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MPEG-2 Encoding Family

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO/IEC 13818. Information technology -- Generic coding of moving pictures and associated audio information (formal name) MPEG-2 (common name)
Description The family of MPEG-2 encodings were 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. Picture, sound, and data elements consist of streams, i.e., the format's sequences of encoded bytes. Elementary streams are the basic element; these are broken 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 stream or are combined with other programs in a multi-program transport stream.
Relationship to other formats
    Has subtype MPEG-2, MPEG-2 Video Encoding (H.262)
    Has subtype MPEG-2_SP, MPEG-2, Simple Profile
    Has subtype MPEG-2_MP, MPEG-2, Main Profile
    Has subtype MPEG-2_422, MPEG-2, 4:2:2 Profile
    Has subtype Other MPEG-2 profiles not documented at this time: SNR Scalable, Spatially Scalable, and High.
    Has subtype D-10, D-10 Video Encoding (IMX)
    Has subtype MP3_ENC, MP3 audio encoding
    Has subtype AAC_MP2, Advanced Audio Coding (MPEG-2)
    Has subtype MPEG_layer_2_audio, MPEG-1 and MPEG-2 Layer II Audio Encoding
    Used by MPEG-2_MP_layer_2, MPEG-2 File with Main Profile Video and Layer II Audio Encoding
    Used by MPEG-2_422_layer_2, MPEG-2 File with 422 Video and Layer II Audio Encoding

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress National Audio-Visual Conservation Center, Packard Campus, at Culpeper, Virginia, has received significant numbers of MPEG-2 files for their holdings as a part of two important retrospective collections. MPEG-2 is used as the "mezzanine" computer-file format for reformatted video recordings, e.g., from VHS tapes, in the American Folklife Center Veterans History Project.
LC preference Content received as MPEG-2 files will be held in this format for the near term although there is discussion of future migrations into MXF_OP1a_JP2_LL, the format currently being employed by the Packard Campus facility as an archival master when reformatting videotapes.

Sustainability factors Explanation of format description terms

Disclosure Open standard. Developed through ISO technical program JTC 1/SC 29 for coding of audio, picture, multimedia and hypermedia information by Working Group 11 (WG11) aka the Moving Picture Experts Group (MPEG). The video coding aspects were co-developed with the International Telecommunication Union (ITU) Telecommunication Standardization Sector (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.

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 patents Managed by MPEG LA LLC (http://www.mpegla.com/main/default.aspx). 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 MPEG-2 shares with MPEG-4 elements of a standardized Intellectual Property Management and Protection (IPMP) scheme; see Intellectual Property Management and Protection in MPEG Standards.

Quality and functionality factors Explanation of format description terms

Moving Image
Normal rendering Good support.
Clarity (high image resolution) Moderate to very good, given that this is a format for lossy compression. Outcome will depend on the type and extent of compression, and the encoder used.
Functionality beyond normal rendering The MPEG-2 transport stream permits the multiplexing of multiple programs.
Sound
Normal rendering Good support.
Fidelity (high audio resolution)

Moderate to very good, given that the options for audio employ lossy 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.

Multiple 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 rendering None

File type signifiers and format identifiers Explanation of format description terms

Tag 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.
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.

Notes Explanation of format description terms

General  
History MPEG stands for the Moving Picture Experts 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).

Format specifications Explanation of format description terms


Useful references

URLs

1 The italicized blurbs in the specifications section are derived from the Berkeley Multimedia Research Center. This link is to the Internet Archive's saved copy of this page: MPEG-2 FAQ


Last Updated: Monday, 27-Feb-2017 09:55:30 EST