An Motion Picture Experts Group-4 (MPEG-4 or MP4) file is a compressed video file that is capable of containing a high-quality film in a small storage space. In many ways, MP4 is similar to the Motion Picture Experts Group-3 (MP3) audio file format, except that it is normally used for video. Many video players are compatible with MP4 format files, and non-compatible programs can read the files with the aid of a tool called a codec.
The need for audio and video compression came along with the need to transfer large audio and video files quickly and efficiently. To overcome this issue, the mass of information contained in an audio or video file is translated into a more succinct and transferable language. This language then becomes known as a “file format,” and as long as the program that is being used is capable of reading that file format, then any file in that format can be translated and then played.
A simple analogy would be the term “MP4” itself. To aid fast communication, the phrase Motion Pictures Expert Group-4 has been compressed into a shortened version. People who are familiar with the subject hear the shortened version “MP4” but fully understand that it is referring to the Motion Pictures Expert Group’s fourth file format. The MP4 format does basically the same thing with video files, compressing the information into a format that can be read and processed more quickly.
The word “codec” comes from the words "compression" and "decompression," which is essentially what they do. An MP4 codec is needed to teach any non-compatible player the specific “language” that is used in the file. These codecs are generally distributed in packs, which makes keeping up to date with new file formats much easier, because users can cover all of the most common formats with one download.
MP4 format is more efficient than its predecessor, Motion Picture Experts Group-2 (MPEG-2), and is very widely used. The format allows users to “stream” video content from the Internet, playing the video content while the file is being downloaded to the user's computer’s hard drive. The format has made video files so much more easily transferable that it is common for portable devices to be capable of storing hours of video clips thanks to file compression.
Generally, MP4 format files will be marked by the extension “.mp4” at the end of the file name. There are variations of this, however. The letters “a” and “v” can be added to specify audio and video files, respectively.