RM is a proprietary video container created by RealNetworks Inc. – the pioneers in streaming media over the internet market. This format supports DRM and was widely used to stream video and audio data online in the early 2000s with more than 80% of online streaming was in the RealMedia format. RM is supported by iPhone, Android, Windows and Mac. This container is often used by online radio stations. Nowadays it is still necessary to install Real Player plugin to be able to play RM files on such streaming websites.

AU is a file extension for a sound file format belonging to Sun, NeXT and DEC and used in UNIX. The AU file format is also known as the Sparc-audio or u-law fomat. AU files contain three parts: the audio data and text for a header (containing 24 bytes) and an annotation block.