H.264 video coding standard can achieve considerably higher coding efficiency than previous standards. However, this comes at a cost in considerably increased complexity at the encoder and thus increases the difficulty in hardware implementation. The computation complexity is mainly due to motion estimation in combination of variable block sizes and multi-reference frames.

To achieve the objective of real-time applications, we propose a fast multiple decision horizontal line search (MDHLS) scheme for H.264 and implement it on Equator DSP. The MDHLS mainly contains two parts, one is HLS algorithm and the other is a fast decision scheme for variable block sizes and multi-reference frames. HLS utilizes the 128-bit register of Equator to jointly accelerate SAD calculation and data access. And we employ a fixed search window size in HLS for further reducing SAD calculation. The proposed variable block size algorithm provides a three-stage decision rule to remove unnecessary computations of motion estimation. An early termination decision rule is also developed for multi-reference frame algorithm. Simulation results show MDHLS can achieve up to 98% cycle reduction in motion estimation implemented on Equator DSP and the coding efficiency is only slightly decreased.