| Full name | ISO/IEC 14496-3:2001. Information technology -- Coding of audio-visual objects -- Part 3: Audio (formal name for the relevant part of the MPEG-4 standard; note that this part covers several types of audio coding including Advanced Audio Coding).
AAC (common name) |
| Description | Perceptual audio encoding format designed for efficient distribution of sound files over moderate bandwidth connections; may be used at higher data rates for better fidelity. AAC_MP4 compression is a further refinement of AAC_MP2. AAC_MP4 is an object-based coding standard; decoders for AAC_MP2 may not be able to read AAC_MP4.
The specification defines various object types and profiles; see Notes. The video-capable iPod introduced in late 2005 specifies video files for which the audio appears to be audio-object-limited rather than profile-compliant; see AAC_MP4_LC. The compiler of this pages welcomes comments on this detail. |
| Production phase | Generally used for final-state, end-user delivery. |
| Relationship to other formats | |
| Supertype of | Various AAC_MP4 profiles, not documented at this time; see Notes. |
| Supertype of | AAC_MP4_LC, AAC Low Complexity Object |
| Used by | MP4_FF_2_AAC, MPEG-4 File Format, V.2, with Advanced Audio Coding |
| Used by | QTA_AAC, QuickTime AAC |
| Used by | MP4_FF_2_V, MPEG-4 File Format, Version 2, with Visual Coding |
| Used by | MP4_FF_2_AVC, MPEG-4 File Format, Version 2, with Advanced Video Coding |
| Used by | MP4_FF_2_AVC_BP, MPEG-4 File Format, V.2, with AVC, Baseline Profile |
| Used by | MP4_FF_2_AVC_MP, MPEG-4 File Format, V.2, with AVC, Main Profile |
| Used by | MP4_FF_2_AVC_EP, MPEG-4 File Format, V.2, with AVC, Extended Profile |
| Used by | MP4_FF_2_AVC_HP, MPEG-4 File Format, V.2, with AVC, High Profile |
| Used by | MP4_FF_2_AVC_H10P, MPEG-4 File Format, V.2, with AVC, High 10 Profile |
| Used by | MP4_FF_2_AVC_H422P, MPEG-4 File Format, V.2, with AVC, High 4:2:2 Profile |
| Used by | MP4_FF_2_AVC_H444P, MPEG-4 File Format, V.2, with AVC, High 4:4:4 Profile |
| Used by | MP4_FF_AVCE_AVCE, MPEG-4 File Format for AVC (Ext), with Non-FRExt Extended AVC Coding |
| Used by | Other file or wrapper formats, not documented at this time |
| 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. |
| Documentation | ISO/IEC 14496-3:2001. Information technology -- Coding of audio-visual objects -- Part 3: Audio. See also MP4_FF_2. |
| Adoption | Some adoption for World Wide Web dissemination and playback on specialized devices. QTA_AAC, QuickTime AAC, is used in Apple's iTunes service. Software tools exist for encoding and decoding. |
| Licensing and patent claims | Royalties are due on the sale of AAC encoders and/or decoders; no use-based fees; information at Via Licensing. |
| Transparency | Depends upon algorithms and tools to read; requires sophistication to build tools. |
| Self-documentation | Technical (coding) information is contained in the headers for the "frames" that make up the bitstream. See also MP4_FF_2. |
| External dependencies | Surround sound requires appropriate amplifier and loudspeakers or headphone. |
| Technical protection considerations | See MP4_FF_2. |
| Normal rendering | Good support. |
| Fidelity (support for high audio resolution) | Moderate to good, given that this is a format for compression. All commentators state that at a given data rate, the quality of AAC_MP4 surpasses AAC_MP2 and is significantly better than MP3_ENC. |
| Support for multiple sound channels | AAC has provision for up to 48 channels, and supports 5.1 (and 7.1?) surround sound. |
| Support for downloadable or user-defined sounds, samples, and patches | Not investigated at this time. |
| Functionality beyond normal rendering | Not investigated at this time. |
