Page 164 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

Chapter 6

Multiple-Reference Motion

Estimation Techniques

6.1 Overview

To achieve high coding e ciency, Chapter 5 investigated an advanced mo-
tion estimation technique called warping-based motion estimation. This chapter
considers another advanced technique, called multiple-reference motion esti-
mation.
In multiple-reference motion-compensated prediction (MR-MCP), motion
estimation and compensation are extended to utilize more than one reference
frame. The reference frames are assembled in a multiframe memory (or bu&er)
that is maintained simultaneously at encoder and decoder. In this case, in
addition to the spatial displacements, a motion vector is extended to also
include a temporal displacement.
This chapter investigates the prediction gains achieved by MR-MCP. Par-
ticular emphasis is given to coding e ciency at very low bit rates. More
precisely, the chapter attempts to answer the following question: Is the use of
additional bit rate to transmit the extra temporal displacement justi able in
terms of an improved rate-distortion performance? The chapter also examines
the properties of the multiple-reference block-motion )eld and compares them
to those of the single-reference case.
The rest of the chapter is organized as follows. Section 6.2 brie-y re-
views multiple-reference motion estimation techniques. Section 6.3 concen-
trates on the long-term memory multiple-reference motion estimation tech-
nique. The section starts by examining the properties of multiple-reference
block-motion )elds and compares them to those of single-reference )elds. It
then investigates the prediction gains and the e ciency of the long-term mem-
ory technique at very low bit rates. The chapter concludes with a discussion in
Section 6.4.

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