RA (RealAudio) is an audio format released in 1995 by RealNetworks. It uses multiple audio codecs, including high-fidelity music formats and low-bitrate formats. Since its introduction, the RA format has been mainly used by radio stations to stream audio online. Also, up until 2009, the BBC has been using it to stream sounds online.
RealNetworks RealPlayer Cloud VLC Media Player Wensites with the RealPlayer Plugin
AC3 is an audio format designed by Dolby Digital to offer surround sound listening. This format is available on most Blu-ray and DVD media files and is played using a Dolby Digital DVD Player. Interestingly, AC3 can be output in up to six speakers of a home stereo system. On a computer, AC3 can be opened on VLC Media Player, Apple QuickTime Player, and Windows Media Player.
VLC Media Player Apple QuickTime Player Windows Media Player