Abstract:  In order to improve the encoding efficiency, this paper proposes a fast CU(Codizy Unit) depth
selection algorithm. First, the MPD(Mean Prediction Depth) of current CU is calculated and then the current
CU is classified based on MPD so as to reduce the redundant traversal. Secondly, the CU depth of current CU is
judged further for stop based on the ratio of the RD(Rate Distortion) cost of the collocated CU col (Co-located CU)
with the reference frame to the total sum of depth. Experimental result shows that the proposed method decreases
the average encoding time by 59% under the condition of decreasing bit rate by 0. 10% and decreasing PSNR by
0. 08 dB,while compared with the reference algorithm in this paper, the encoding time is reduced by 11% on
average, and decreases the encoding complexity and improves the encoding efficiency.

Key words: inter-frame prediction, depth selection,  high efficiency video coding (HEVC)