Mobile Intelligence

23.2 VIDEO CODEC

For fast transmission and easy storage, video is encoded or compressed by codecs. Here we briefly introduce the popular codecs that are used to encode video to be replayed on the handheld device in the experiment.

23.2.1 MPEG-4

MPEG-4 was issued in 1998. It consists of a series of audio and video code standards and a set of relevant technology. Its formulation organization is ISO/IEC Moving Pictures Experts Group, namely MPEG. MPEG-4 includes most functions of MPEG-1 and MPEG-2 and strong features of other formats. It adds and expands supports for the Virtual Reality Model Language, the object-oriented synthetic files (including audio, video, and VRML Object), and the Digital Rights Management and other interactive functions. Most functions of MPEG-4 are decided or adopted by the developer. This means that the whole function is not concluded by certain procedure. So, this form uses the so-called “profiles” and “levels” to define some specific sets of functions for certain applications of MPEG-4 [3, 4].

23.2.2 DivX

DivX is the name of products by Div, Inc. Basically Microsoft's encoders do not allow users to save MPEG-4 streams into the AVI format and force users to use ASF instead. They also have some other limitations that are overridden in DivX. Many newer “DivX Certified” DVD players are able to play video coded by DivX. The Quarter pixel (QPEL) and Global Motion Compensation (GMC) features are often omitted to reduce processing requirements, so for compatibility ...