H.264/AVC belongs to block-based coding category. For the H.264/AVC intraframe coding, a frame is first divided into non-overlapped blocks, and then intra prediction and the DCT-like transform are applied block by block. For the inter frame coding, H.264/AVC employs variable-block-size for motion compensation and transform stages that can significantly improve the coding performance compared with previous video coding standards. However, for the transform stage of intraframe coding, H.264/AVC only provides two fixed transform block sizes: 4 × 4 and 8 × 8 blocks. In this paper, we propose to employ two massive dictionaries (dyadic and multitree) of representations to improve the efficiency of H.264/AVC intraframe coding. In addition, the corresponding rate-distortion cost function and a fast search algorithm are introduced to incorporate the massive dictionaries into the transform stage. The experimental results show that the proposed method outperforms H.264/AVC in terms of both subjective and objective evaluations.