A method of encoding, comprising: developing a plurality of motion vectors indicating relative movements of regions from a reference image frame to form a corresponding region in a second image frame to be encoded wherein each said region comprises a block; wherein said block is obtained by partitioning a 16x16 source block into blocks of size 16x16, 8x8, 4x8, 8x4 and 4x4, each of which corresponding to blocks of a particular partitioning and wherein motion vectors are developed for each block of each partitioning of said 16x16 source block; for each motion vector, developing a respective measure of distortion between corresponding blocks of the image frames; for each motion vector, developing a respective measure of bit cost of developing the motion vector; determining a maximum number of allowed motion vectors; said encoding method further comprising the steps of: a) for each of the first to the fourth 8x8 blocks of pixel data of the 16x16 source block, pre-selecting one partitioning out of the two partitionings with two motion vectors using rate-distortion selection, and retaining three partitionings, said three partitionings comprising one partitioning with four motion vectors, corresponding to the partitioning of the 8x8 block into four 4x4 blocks, one partitioning with two motion vectors, corresponding to one of the partitionings into two 8x4 blocks or into two 4x8 blocks; and one partitioning with one motion vector, corresponding to the partitioning of the 8x8 block into one 8x8 block; b) combining the three retained partitionings of each of the groups consisting of the first and second 8x8 blocks and consisting of the third and fourth 8x8 blocks, respectively, wherein for each group when two or more of the obtained combinations of partitionings have the same total number of motion vectors, pre-selecting to keep only one partitioning with the same total number of motion vectors, such that six partitionings are retained for each group; c) combining the six retained partitionings of the two said groups, wherein when two or more of the obtained partitions have the same total number of motion vectors, pre-selecting to keep only one partitioning with the same total number of motion vectors; d) for the block of 16x16 pixel data pre-selecting one partitioning out of the two partitionings with two motion vectors and retaining two partitionings, said two partitionings comprising one partitioning with two motion vectors, corresponding to partitioning of the 16x16 block into two 8x16 blocks or into two 16x8 blocks and one partition with one motion vector, corresponding to the partioning of the 16x16 source block into one 16x16; using rate-distortion optimisation to select among all retained partitionings the partitioning which minimises said distortions and said costs to perform estimation, the number of motion vectors of the selected partitioning being less than the maximum number of motion vectors. developing a plurality of motion vectors indicating relative movements of regions from a reference image frame to form a corresponding region in a second image frame to be encoded wherein each said region comprises a block; wherein said block is obtained by partitioning a 16x16 source block into blocks of size 16x16, 8x8, 4x8, 8x4 and 4x4, each of which corresponding to blocks of a particular partitioning and wherein motion vectors are developed for each block of each partitioning of said 16x16 source block; for each motion vector, developing a respective measure of distortion between corresponding blocks of the image frames; a) for each of the first to the fourth 8x8 blocks of pixel data of the 16x16 source block, pre-selecting one partitioning out of the two partitionings with two motion vectors using rate-distortion selection, and retaining three partitionings, said three partitionings comprising one partitioning with four motion vectors, corresponding to the partitioning of the 8x8 block into four 4x4 blocks, one partitioning with two motion vectors, corresponding to one of the partitionings into two 8x4 blocks or into two 4x8 blocks; and one partitioning with one motion vector, corresponding to the partitioning of the 8x8 block into one 8x8 block; b) combining the three retained partitionings of each of the groups consisting of the first and second 8x8 blocks and consisting of the third and fourth 8x8 blocks, respectively, wherein for each group when two or more of the obtained combinations of partitionings have the same total number of motion vectors, pre-selecting to keep only one partitioning with the same total number of motion vectors, such that six partitionings are retained for each group; c) combining the six retained partitionings of the two said groups, wherein when two or more of the obtained partitions have the same total number of motion vectors, pre-selecting to keep only one partitioning with the same total number of motion vectors; d) for the block of 16x16 pixel data pre-selecting one partitioning out of the two partitionings with two motion vectors and retaining two partitionings, said two partitionings comprising one partitioning with two motion vectors, corresponding to partitioning of the 16x16 block into two 8x16 blocks or into two 16x8 blocks and one partition with one motion vector, corresponding to the partioning of the 16x16 source block into one 16x16;