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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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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