Dynamic reference motion vector coding mode

An apparatus for decoding a video bitstream, comprising:

• a processor configured to perform a method comprising:
• identifying, for respective previously coded blocks of a plurality of previously coded blocks, a candidate motion vector used to inter predict the previously coded block to define a plurality of candidate motion vectors;
• determining, for each candidate motion vector of the plurality of candidate motion vectors, a distance between the previously coded block associated with the candidate motion vector and a current block of a current frame;
• determining, for each candidate motion vector of the plurality of candidate motion vectors, a popularity value based on a set of previously coded pixels associated with the candidate motion vector;
• for decoding the current block using compound prediction, determining a first reference frame and a second reference frame;
• ranking each candidate motion vector of the plurality of candidate motion vectors within a list of candidate reference motion vectors according to a priority value for each candidate motion vector, the priority value based on the distance and the popularity value associated with the candidate motion vector, wherein for decoding the current block using compound prediction, ranking each candidate motion vector comprises:
• determining reference blocks of the plurality of previously coded blocks that share the first reference frame and the second reference frame:
• and
• assigning a higher priority to candidate motion vectors from the reference blocks of the plurality of previously coded blocks that share a same combination of the first reference frame and the second reference frame within the list of candidate reference motion vectors than combinations of candidate motion vectors from others of the plurality of previously coded blocks encoded using respective single reference frames of the first reference frame and the second reference frame;
• selecting, from the list, a reference motion vector;
• and
• decoding the current block using the reference motion vector.