MPEG-4 Audio Object Types
MPEG-4 Audio includes a system for handling a diverse group of audio formats in a uniform manner. Each format is assigned a unique Audio Object Type to represent it. Object Type is used to distinguish between different coding methods. It directly determines the MPEG-4 tool subset required to decode a specific object. The MPEG-4 profiles are based on the object types and each profile supports different list of object types.
| Object Type ID | Audio Object Type | First public release date | Description |
|---|---|---|---|
| 1 | AAC Main | 1999 | contains AAC LC |
| 2 | AAC LC (Low Complexity) | 1999 | Used in the "AAC Profile". MPEG-4 AAC LC Audio Object Type is based on the MPEG-2 Part 7 Low Complexity profile (LC) combined with Perceptual Noise Substitution (PNS) (defined in MPEG-4 Part 3 Subpart 4). |
| 3 | AAC SSR (Scalable Sample Rate) | 1999 | MPEG-4 AAC SSR Audio Object Type is based on the MPEG-2 Part 7 Scalable Sampling Rate profile (SSR) combined with Perceptual Noise Substitution (PNS) (defined in MPEG-4 Part 3 Subpart 4). |
| 4 | AAC LTP (Long Term Prediction) | 1999 | contains AAC LC |
| 5 | SBR (Spectral Band Replication) | 2003 | used with AAC LC in the "High Efficiency AAC Profile" (HE-AAC v1) |
| 6 | AAC Scalable | 1999 | |
| 7 | TwinVQ | 1999 | audio coding at very low bitrates |
| 8 | CELP (Code Excited Linear Prediction) | 1999 | speech coding |
| 9 | HVXC (Harmonic Vector eXcitation Coding) | 1999 | speech coding |
| 10 | (Reserved) | ||
| 11 | (Reserved) | ||
| 12 | TTSI (Text-To-Speech Interface) | 1999 | |
| 13 | Main synthesis | 1999 | contains Wavetable synthesis and Algorithmic Synthesis and Audio Effects |
| 14 | Wavetable synthesis | 1999 | contains General MIDI |
| 15 | General MIDI | 1999 | |
| 16 | Algorithmic Synthesis and Audio Effects | 1999 | |
| 17 | ER AAC LC | 2000 | Error Resilient |
| 18 | (Reserved ) | ||
| 19 | ER AAC LTP | 2000 | Error Resilient |
| 20 | ER AAC Scalable | 2000 | Error Resilient |
| 21 | ER TwinVQ | 2000 | Error Resilient |
| 22 | ER BSAC (Bit-Sliced Arithmetic Coding) | 2000 | It is also known as "Fine Granule Audio" or fine grain scalability tool. It is used in combination with the AAC coding tools and replaces the noiseless coding and the bitstream formatting of MPEG-4 Version 1 GA coder. Error Resilient |
| 23 | ER AAC LD (Low Delay) | 2000 | Error Resilient, used with CELP, ER CELP, HVXC, ER HVXC and TTSI in the "Low Delay Profile", (commonly used for real-time conversation applications) |
| 24 | ER CELP | 2000 | Error Resilient |
| 25 | ER HVXC | 2000 | Error Resilient |
| 26 | ER HILN (Harmonic and Individual Lines plus Noise) | 2000 | Error Resilient |
| 27 | ER Parametric | 2000 | Error Resilient |
| 28 | SSC (SinuSoidal Coding) | 2004 | |
| 29 | PS (Parametric Stereo) | 2004 and 2006 | used with AAC LC and SBR in the "HE-AAC v2 Profile". PS coding tool was defined in 2004 and Object Type defined in 2006. |
| 30 | MPEG Surround | 2007 | also known as MPEG Spatial Audio Coding (SAC), it is a type of spatial audio coding (MPEG Surround was also defined in ISO/IEC 23003-1 in 2007) |
| 31 | (Reserved) | ||
| 32 | MPEG-1/2 Layer-1 | 2005 | |
| 33 | MPEG-1/2 Layer-2 | 2005 | |
| 34 | MPEG-1/2 Layer-3 | 2005 | also known as "MP3onMP4" |
| 35 | DST (Direct Stream Transfer) | 2005 | lossless audio coding, used on Super Audio CD |
| 36 | ALS (Audio Lossless Coding) | 2006 | lossless audio coding |
| 37 | SLS (Scalable Lossless Coding) | 2006 | two-layer audio coding with lossless layer and lossy General Audio core/layer (e.g. AAC) |
| 38 | SLS non-core | 2006 | lossless audio coding without lossy General Audio core/layer (e.g. AAC) |
| 39 | ER AAC ELD (Enhanced Low Delay) | 2008 | Error Resilient |
| 40 | SMR (Symbolic Music Representation) Simple | 2008 | note: Symbolic Music Representation is also the MPEG-4 Part 23 standard (ISO/IEC 14496-23:2008) |
| 41 | SMR Main | 2008 | |
| 42 | USAC (Unified Speech and Audio Coding) (no SBR) | under development | |
| 43 | SAOC (Spatial Audio Object Coding) | 2010 | note: Spatial Audio Object Coding is also the MPEG-D Part 2 standard (ISO/IEC 23003-2:2010) |
| 44 | LD MPEG Surround | 2010 | This object type conveys Low Delay MPEG Surround Coding side information (that was defined in MPEG-D Part 2 - ISO/IEC 23003-2) in the MPEG-4 Audio framework. |
| 45 | USAC | under development (it will be also defined in MPEG-D Part 3 - ISO/IEC 23003-3) |
Read more about this topic: MPEG-4 Part 3
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