rmvb The .rmvb filename extension refers to the RealMedia variable bitrate format which is an extension of the RealMedia multimedia container format. RMVB is a proprietary multimedia digital container developed and maintained by RealNetworks, an internet streaming Media Company. It is different from its closely related format .rm in that it was designed for distribution of complete multimedia content, however it does support real-time media streaming. Video and Audio streams can be encoded and packaged into this format and distributed as single files for later playback on compatible devices and software as opposed to file streaming on high bandwidth networks.
ac3 Files with the .ac3 filename extension refer to the proprietary audio file format Dolby digital AC-3, developed by Dolby Laboratories. The AC-3 format is from the lossy family of audio compression formats. It supports a variety of audio channel configurations and was the first of its kind to support the full surround sound experience. Because of this, the format has been commonly used in the development of motion picture features designed for theaters and in consumer homes through DVDs and surround sound home theater systems. The AC-3 format is one of the supported audio codecs of the ATSC standard ' a set of standards developed for digital television transmission in several affiliated countries.