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Learn about enhanced video encoding

Posted: 01 Aug 2008     Print Version  Bookmark and Share

Keywords:motion compensation  motion estimation  video compression algorithm  video encoding 

A video consists of sequences of still pictures in time. When these still pictures are displayed exactly at the same rate they are captured, they give the impression of a video. This principle has been used for about 100 years in movie production and displays. Although the same principle is applicable to digital video, some new challenges come up. Before going into digital video, let's consider the case of a digital image. A digital image compression scheme such as JPEG can't be used for video just because the data rate produced by this method is still very high. This arises due to the fact that a video consists of about 30fps. The higher bit rate arises due to the fact that in a video sequence one frame has lot of correlation with the previous frames. Unfortunately, JPEG does not exploit this redundancy. This redundancy in time domain is known as the temporal redundancy.

Motion compensation is the process in which a portion or block of a current frame is predicted from a portion from the past frame. Motion estimation (ME) is process of finding the right candidate in the past frame (reference frame) for the replacement. Motion compensation involves only a replacement, while ME involves finding the right candidate. Therefore, ME is a computationally demanding process. A better ME always means less residual code and hence means better video coding efficiency.

The goal of a video compression algorithm is to reduce the data used to represent the original video without compromising perceptual quality of the compressed video.

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