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.
avi The AVI file format is one of the most widely used multimedia containers ever devised. AVI, which stands for audio video interleaved, was first introduced to the public by Microsoft in 1992 as part of their 'video for windows' multimedia framework. Being a container format, an AVI file with the .avi filename extension can exist with both video and audio content synchronized for playback. The format can thus be used by authors to edit and encode audio video sequences or just video sequences. The Digital video AVI format exists in two forms, Type 1 and Type 2.