Video Codec - definition
A video codec is the part of the software that handles converting stored digital information back to images and vice-versa. Different codecs have different capabilities, making them suitable for different applications.
Regular feature phones come with a fixed set of video codecs, while the capability of smartphones to playback different codecs can usually be expanded by installing third-party solutions.
The most popular mobile codecs are H.263 used in 3GP videos, H.264 in MPEG4 videos, and DivX and XviD for avi files.