Keyframes are still images

which best represent the content of the video sequence in an abstracted manner

and may be extracted from original compressed data. Keyframes are frequently used to supplement the text of a video log

but there has been little progress in identifying them automatically. The challenge is that the extraction of keyframes needs to be automatic and content based so that they maintain the important content of the video while removing all redundancy. Up to now

more and more video materials are stored and transmitted in the compression data

so it is practical to study a unified approach to extraction of keyframes based on compressed video data. In this paper

we present a system for extraction of keyframes

which is based on different formulae comparing discrete cosine transform(DCT) direct current(DC) coefficients over the I frames in MPEG video stream

and for which only minimal decoding is needed. In theory semantic primitives of the video

such as interesting objects

actions and events should be used. However

because such general semantic analysis is not currently feasible

we explore two methods instead

in which one is from the idea of dot in mass

and the other is based on the number of unequal macro blocks.