RVMB is a file type developed by Real Networks and stands for RealMedia Variable Bit Rate file. RMVB is quite similar to MPEG4 files and differs from the RealMedia format which encodes at a constant value. XVID and DIVX are other types of variable bitrate files. RMVB files are quite common in Asia but less prevalent in Europe and the Americas.
Variable bit rate files alter the amount of data for a given amount of time. This allows the bitrate to be increased for more complex elements of the file, and decreased for less complex parts. This means the storage requirements of the file are less with a negligible decrease in image and audio quality. The disadvantage of this type of file is that the encoding process is longer compared to a constant bitrate file.
MP4 files (MPEG-4 Part 14) are multimedia files. MP4 is a container format that can store video, audio and subtitle data (as well as more depending on content). Since stores like iTunes uses this container format, and it is used with iPod and PlayStation Portable (PSP), MP4 files have become more common.
MPEG-4 Part 14 or MP4, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.
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