In this paper, a multihypothesis prediction scheme for inter frame video coding is proposed. Using a template matching algorithm, motion vectors are derived at the decoder side instead of explicitly coding the motion vectors into the bitstream. Therefore, higher numbers of hypotheses can be used in the averaging process at no additional coding cost. The proposed scheme has been implemented into the H.264/AVC reference software. Simulation results show bitrate reductions compared to H.264/AVC of 7.7% on average for the tested video sequences. It is shown that part of the performance gain is due to rounding effects in H.264/AVC sub-pixel interpolation which can be exploited in the averaging calculation of the proposed multihypothesis prediction. Experiments with an improved interpolation filter for both reference scheme and the proposed scheme still yield bitrate reductions of 4.7% on average.
Decoder-side motion vector derivation (DMVD) using template matching has been shown to improve coding efficiency of H.264/AVC based video coding. Instead of explicitly coding motion vectors into the bitstream, the decoder performs motion estimation in order to derive the motion vector used for motion compensated prediction. In previous works, DMVD was performed using a full template matching search in a limited search range. In this paper, a candidate based fast search algorithm replaces the full search. While the complexity reduction especially for the decoder is quite significant, the coding efficiency remains comparable. While for the full search algorithm BD-bitrate savings of 7.4% averaged over CIF and HD sequences according to the VCEG common conditions for IPPP high profile are observed, the proposed fast search achieves bitrate reductions of up to 7.5% on average. By further omitting sub-pel refinement, average savings observed for CIF and HD are still up to 7%
The ongoing increase of computing performance facilitates a higher algorithmical complexity in video coding systems. The decoder may be able to estimate or derive prediction parameters based on the previously decoded signal. In this paper we present an extension to H.264/AVC where the explicit coding of motion parameters is adaptively replaced by a template matching algorithm that is performed identically at the encoder and decoder. The decision between explicit coding and derivation of motion parameters is done by the rate-distortion optimised mode decision and coded into the bitstream. Compared to previous work, the provided scheme has been extended to bidirectional prediction (B pictures). Simulation results show an improved coding efficiency over a wide range of test sequences, especially for higher spatial resolutions.
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