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.
mpg Some confusion exists in whether there is an underlying difference between the filename extension .mpg and .mpeg. The short answer is there is no difference. Both filename extensions refer to one of two MPEG standards either MPEG-1 or MPEG-2. The reason for the confusion has its history in how early versions of windows enforced a maximum of three characters for filename extensions whereas Mac OS did not have such limitations. Thus on windows the mpeg file format was referred to using the .mpg filename extension whereas on Mac OS the filename extension .mpg and .mpeg was used interchangeably but referred to the same file format. The format is still the most broadly compatible audio and video container format from the lossy class of containers. The MPEG standard is supported by numerous audio and video products and software applications.