System for nested entropy encoding

1. An apparatus for decoding a motion vector of a current block in a sequence of pictures encoded in a bitstream of coded pictures, the apparatus comprising processing circuitry to perform operations comprising:

obtaining the bitstream of coded pictures;

obtaining, from the bitstream, a flag that indicates whether candidate motion vector trimming is to be applied when decoding the bitstream of coded pictures;

determining that the flag indicates that candidate motion vector trimming is to be applied when decoding the bitstream of coded pictures and, in response:

identifying a first adjacent block and a second adjacent block which are adjacent to the current block in a current picture;

constructing a set of candidate motion vector predictors comprising motion vectors of the first and second adjacent blocks;

determining whether the motion vectors of the first and second adjacent blocks are identical;

when the motion vectors of the first and second adjacent blocks are identical:

removing the motion vector of the second adjacent block from the set of candidate motion vector predictors, and

adding a motion vector of a block in a previously decoded picture to the set of candidate motion vector predictors, wherein the block in the previously decoded picture that is added to the set of candidate motion vector predictors for the current block is larger than the current block;

selecting one of the motion vectors in the set of the candidate motion vector predictors as the motion vector predictor of the current block; and

deriving the motion vector of the current block based on the selected motion vector predictor.

2. The apparatus of claim 1 , wherein the block in the previously decoded picture is a grouping of smaller blocks in the previously decoded picture.

3. The apparatus of claim 2 , wherein the motion vector of the block in the previously decoded picture is an average of motion vectors of the smaller blocks in the previously decoded picture.