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.
AVI stands for Audio Video Interleave. Files of this format have an .avi extension. Developed by Microsoft in 1992, it has become so widespread that many people consider it the de-facto standard for storing video and audio information on PC. AVI combines audio and video into a single file in a standard container to allow simultaneous playback. Its advatage is a simple architecture, due to which AVI runs on a number of different systems like Windows, Mac, Linux, Unix and is supported by all of the most popular web-browsers.'
AVI is a derivative of the Resource Interchange File Format (RIFF), which divides a file's data into blocks, or chunks. Each chunk is identified by a FourCC tag. An AVI file takes the form of a single chunk in a RIFF formatted file, which is then subdivided into two mandatory chunks and one optional chunk. The first sub-chunk is identified by the hdrl tag. This sub-chunk is the file header and contains metadata about the video, such as its width, height and frame rate. The second sub-chunk is identified by the movi tag. This chunk contains the actual audio/visual data that make up the AVI movie. The third optional sub-chunk is identified by the idx1 tag which indexes the offsets of the data chunks within the file.
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