(registered 2018-04-06, last updated 2018-04-06) Type name: audio Subtype name: aac Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary Files are encoded binary MPEG-4 Advanced Audio Coding (AAC) media packed in one of the following MPEG-4 audio formats: 1) Low Overhead Audio Transport Multiplex / Low Overhead Audio Stream (LATM/LOAS) as defined in ISO/IEC 14496-3 2) Audio Data Transport Stream (ADTS) as defined in ISO/IEC 14496-3 Receivers can distinguish the two by inspecting the binary data stream and searching for the syncwords as listed below: 1) Syncword for LOAS AudioSyncStream() 0x2B7 (11bit sequence) 2) Syncword for LOAS EPAudioSyncStream() 0x4DE1 (16bit sequence) 3) Syncword for ADTS adts_sequence() 0xFFF (12bit sequence) The syncword should be the first bits that are received from a server when requesting data identified with this mime type. Encoded audio files packed in LATM/LOAS format should have the file extension ".loas". Encoded audio files packed in ADTS format should have the file extension ".aac". Files shall be transmitted without CR/LF conversion, 7-bit stripping, or any other modification to the binary data. Files may contain ID3v2.x frames at any frame boundary. For use over the Internet, it is assumed that lower layers take care of transmission errors, so audio/aac data may include frames without the optional cyclic redundancy check (CRC). The AAC audio data is binary data, and must be specifically encoded for non-binary transport; the Base64 encoding is suitable when attaching to Email. Note that the MPEG audio data typically does not yield further compression when using file-based lossless compression, e.g. zip. Security considerations: AAC is a tagged data format, and some tags are available for private use (e.g. the Data Stream Element). As such, arbitrary material could potentially be transferred in the AAC stream, including executable content. Tagged data containing executable content should never be sent and must not be executed if it is received. Note: The requirement that such content must not be executed on receipt is especially important since situations exist where content will be generated independently and therefore could contain executable content that the sender or receiver is unaware of. It is the responsibility of the decoder/player client to respect and apply appropriate file security and protection against any potential malicious content. AAC is an algorithm that can drastically reduce and compress audio data and hence audio/aac objects represent compressed data. Conversely, depending on the previously applied compression factor, decoding / uncompressing this data can lead to a significant growth in data size. audio/aac objects are not signed or encrypted internally. External security mechanisms must be employed to ensure content confidentiality and integrity. Interoperability considerations: The AAC family of codec technologies is specified in ISO/IEC 13818-7 as AAC LC Profile, in ISO/IEC 14496-3 as AAC, HE-AAC and HE-AAC v2 Profiles. Implementations of the AAC family of technologies have reference software for reading and writing the file format and are available for a variety of computer platforms. Published specification: ISO/IEC 14496-3 ISO/IEC 13818-7 Applications that use this media type: Advanced Audio Coding (AAC) audio is device, platform, and vendor neutral and is supported by a wide range of encoders and decoders/players, for example for Multimedia, HLS Audio-Only Streams - IETF HTTP Live Streaming, SHOUTcast/Icecast2 Audio Streams. Fragment identifier considerations: N/A Additional information: Deprecated alias names for this type: N/A Magic number(s): N/A File extension(s): .adts or .aac (ADTS), .loas or .ass (LATM/LOAS) Macintosh file type code(s): N/A Person & email address to contact for further information: Max Neuendorf max.neuendorf&iis.fraunhofer.de Intended usage: Common Restrictions on usage: N/A Author: Max Neuendorf max.neuendorf&iis.fraunhofer.de Change controller: ISO/IEC JTC1/SC29/WG11 ("MPEG")