Advanced Audio Coding - Container Formats

Container Formats

In addition to the MP4, 3GP and other ISO base media file format-based container formats for file storage, AAC audio data was first packaged in file based form for the MPEG-2 standard by using a more basic format called Audio Data Interchange Format (ADIF), consisting of a single header followed by the raw AAC audio data blocks. However if the data is to be streamed within a MPEG-2 transport stream a self synchronizing format called an Audio Data Transport Stream (ADTS) is used, consisting of a series of frames, each frame having a header followed by the AAC audio data. This file and streaming based format are defined in MPEG-2 Part 7, but are only considered informative by MPEG-4, so an MPEG-4 decoder does not need to support either format. These containers, as well as a raw AAC stream, may bear the .aac file extension. MPEG-4 Part 3 also defines its own self synchronizing format called a Low Overhead Audio Stream (LOAS) that encapsulates not only AAC, but any MPEG-4 audio compression scheme such as TwinVQ and ALS. This format is what was defined for use in DVB transport streams when encoders use either SBR or parametric stereo AAC extensions, however it is restricted to only a single non-multiplexed AAC stream. This format is also referred to as a Low Overhead Audio Transport Multiplex (LATM), which just an interleaved multiple stream version of a LOAS.