Sustainability of Digital Formats
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Identification and description

Full name	Information technology -- Coding of audio-visual objects (formal name) MPEG-4, Visual Coding, Main Profile
Description	See also MP4_FF_2 and MPEG-4_V. Created to serve broadcast services, permitting the highest quality, and supporting arbitrarily shaped objects using grayscale coding.1 The Main Profile permits the use of the following visual object types: • Simple: rectangular video, uses intra (I) and predicted (P) video object planes (VOPs, the MPEG-4 term for frames). • Core: arbitrarily shaped video, uses a tool superset of Simple, adds bidirectional (B) video object planes (VOPs), binary shape coding, and supports temporal scalability based on sending extra P-VOPs. • Main: arbitrarily shaped video, adds to Core the coding of grayscale shapes, sprites (object in memory with all pixel information, e.g., the background of scene), and interlaced coding. • Scalable Texture: arbitrarily shaped still image with wavelet compression and incremental download. Three compression levels are permitted; the highest accepts up to 32 objects (Simple, Core, or Main) for a maximum total bit rate of 38 Mbps.
Production phase	Generally a final-state (end-user delivery) format.
Relationship to other formats
Subtype of	MPEG-4_V, MPEG-4, Visual Coding (Part 2)
Used by	MP4_FF_2_V, MPEG-4 File Format, V.2, with Visual Coding (All Profiles)

Local use

LC experience or existing holdings
LC preference

Sustainability factors

Disclosure	Open standard. See MP4_FF_2.
Documentation	See MP4_FF_2.
Adoption	Actual adoption not known to the compilers of this document.
Licensing and patents	See MP4_FF_2.
Transparency	See MP4_FF_2.
Self-documentation	See MP4_FF_2.
External dependencies	See MP4_FF_2.
Technical protection considerations	See MP4_FF_2.

Quality and functionality factors

Moving Image
Normal rendering	Good support.
Clarity (high image resolution)	See MPEG-4 and MPEG-4_V. Potential for greater clarity at a given picture size, data rate, and encoding algorithm, than some other MPEG-4 profiles, e.g., Simple, Simple Scalable, Advanced Simple, and Core Profiles.
Functionality beyond normal rendering	See MPEG-4.

File type signifiers

Tag	Value	Note
Filename extension	mp4
Internet Media Type	See note	See MP4_FF_2
Magic numbers	See note	See MP4_FF_2
File type brand (ISO Base Media File Format)	See note	Indicated in file wrapper and relates to "brands" defined in ISO_BMFF. Wrapping MPEG-4_V bitstreams in MP4_FF_1 would occasion the use of mp41; in MP4_FF_2, use mp42. See Part 15 of the standard, pp. 2-9, 13.
Other	00110010, 00110011, 00110100	Profile and level indicators. For profile_and_level_indication for Main Profile, levels 2, 3, and 4. From Annex G of Part 2 of the standard, pp. 454-55.

Notes

General
History

Format specifications

• See Disclosure under Sustainability factors.

Useful references

Books, articles, etc.

• See MP4_FF_2.