ADTS (Audio Data Transport Stream) is a container format for audio data encoded with the Advanced Audio Coding (AAC) encoding scheme, originally introduced with the MPEG-2 specification. The Advanced Audio Coding scheme is a lossy compression scheme, which was developed with the intention of replacing the MP3 encoding format as a standard. However, while AAC-encoded files were achieving better sound quality in smaller file sizes compared to MP3 files at similar bit rates, the MP3 format was supported by a wider range of applications and devices, leaving it in a dominant position.
While AAC can be encountered as a stand-alone extension, AAC-encoded data stored in ADTS files is used particularly for real-time audio streaming in online radio applications and the like. In contrast to other popular streaming formats, an ADTS file consists of series of frames, each containing header data followed by the compressed audio data. This file structure makes the ADTS an ideal audio streaming format, as it makes it easier on software applications to read the stream at any given point of its broadcast.
Since AAC encoding was also featured in the updated MPEG-4 specification, it's not unusual to also discover AAC-encoded audio data stored in MPEG-4 (MP4) container files.