In order to further improve the coding performance of block-based and quadtree-based adaptive loop
filter(BQ ALF) algorithm, fast adaptive loop filter algorithm with the optimal symmetry(FALF OS) is proposed. Firstly,
this algorithm determines the optimal symmetry filter according to area symmetry and average sum of absolute difference.
Then the filter areas are obtained by using the block-based and quadtree-based method in I frame, and the filter areas are
obtained through motion vector, motion estimation and rate distortion optimization model A(RDOA) in P or B frame. Finally,
the filter areas are filtered by the optimal symmetry filter. Simulation results show that compared with BQ ALF algorithm,
the proposed algorithm reduces the coding time greatly, mean while, the reconstructed picture quality it kept