(registered 2018-03-19, last updated 2020-12-23) Type name: audio Subtype name: usac Required parameters: N/A Optional parameters: N/A Encoding considerations: Binary Files are encoded binary MPEG-D Unified Speech and Audio (USAC) media packed in the MPEG-4 audio format Low Overhead Audio Transport Multiplex / Low Overhead Audio Stream (LATM/LOAS) as defined in ISO/IEC 14496-3. 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 LATM/LOAS frame boundary. For use over the Internet, it is assumed that lower layers take care of transmission errors, so audio/usac data may include USAC frames generated without the optional cyclic redundancy check (CRC) data. Bit rate not allocated to CRC data can be allocated to audio data, thus yielding improved audio quality. The USAC 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: USAC is a tagged data format, and some tags are available for private use. As such, arbitrary material could potentially be transferred in the USAC 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. USAC is an algorithm that can drastically reduce and compress audio data and hence audio/usac 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/usac 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, High Efficiency AAC and High Efficiency AAC v2 Profiles, and in ISO/IEC 23003-3 as Extended High Efficiency AAC Profile. 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 23003-3 ISO/IEC 14496-3 ISO/IEC 13818-7 Applications that use this media type: Unified Speech and Audio Coding (USAC) 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): .loas (preferred), .xhe 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/WG6 ("MPEG Audio Coding")