What Is H.264 codec?
H.264 is a new video codec standard which can achieve high quality video in relatively low bitrates. You can think it as the "successor" of the existing formats (MPEG2, MPEG-4, DivX, XviD, etc.) as it aims in offering similar video quality in half the size of the formats mentioned before.
Also known as AVC (Advanced Video Coding, MPEG-4 Part 10), H.264 is actually defined in an identical pair of standards maintained by different organizations, together known as the Joint Video Team (JVT). While MPEG-4 Part 10 is an ISO/IEC standard, it was developed in cooperation with the ITU, an organization heavily involved in broadcast television standards. Since the ITU designation for the standard is H.264, you may see MPEG-4 Part 10 video referred to as either AVC or H.264. Both are valid, and refer to the same standard.