We present a family of new macroblock partitions for H.264/AVC inter prediction. These modes allow a macroblock to be bipartitioned along a horizontal, vertical, or diagonal edge with an arbitrary location within the block. These new partitioning modes allow an encoder to adapt more closely to the local motion characteristics and improve its rate-distortion performance. In order to quantify the improvements we implemented the proposed partitioning modes in the context of the H.264/AVC video coding standard. Over half the coding efficiency of existing more general schemes is attained at a fraction of the number of added partitioning modes, and hence of encoder complexity, of those schemes. The results are consistent across different profiles, indicating that the proposed extension has good compatibility with the existing H.264/AVC tools for motion compensation and residual coding.