Compressing video data reduces the size of files containing video films to make data transmission faster and reduce the space required to store the file in comparison with the uncompressed video format. There are different compression methods; the most commonly used are MPEG and MJPEG.
Examples of compression:
MPEG compression is based on the principle that in a video file, large parts of consecutive images are identical and do not have to be saved in their entirety for every picture. The MPEG codec forms so-called image groups in which the first key picture is saved exactly and the following ones are interpreted. This makes significant data compression possible, but only the key images can be cropped.
With MJPEG compression (= Motion JPEG) on the contrary, each individual image is compressed with JPEG irrespective of the movement. This means that a video clip is coded as a sequence of JPEG images and any image can be cropped. The video recording is high quality and, at 3 MB/sec, corresponds roughly to S-VHS. Most digital video cameras use the MJPEG standard.
Other compression formats are e.g.:
MPEG-1, MPEG-2 and MPEG-4, H.263, H.264/AVC among others.