When MPEG-4 Isn't MPEG-4

摘要

Many people are familiar with what generically is known as MPEG-4 or MP4 video. Popular implementations of this are DivX and Xvid, both of which have found wide use on file-sharing sites. Technically though, DivX and Xvid implement MPEG-4 Part 2. Much like MPEG-2 before it, the MPEG-4 standard encompasses several different audio, video and file format standards. There isn't space to go into too much detail on MPEG-4 here, so see en.wikipedia.org/wiki/MPEG-4 for more information (a lot more). The main point I want to make about MPEG-4 Part 2 is that even though when the first implementations were released it was hailed as an excellent video codec that was far better than MPEG-2 video, MPEG-4 Part 2's two main modes are known as the Simple or Advanced Simple Profiles. In other words, they're the children of the MPEG-4 world. The "all-grown-up" video codec of MPEG-4 is Part 10, which is also known as MPEG-4 AVC (Advanced Video Coding). The International Telecommunications Union calls it H.264.