As High Efficiency Video Coding (HEVC) is a worldwide popular video coding standard, the steganography of HEVC videos has gained more and more attention. Prediction unit (PU) is one of the most important innovative modules of HEVC; thus, PU partition mode-based steganography is becoming a novel branch of HEVC steganography. However, the embedding capacity of this kind of steganography is limited by the types of PU partition modes. To solve the problem, modified exploiting modification direction (EMD)-coded PU partition mode-based steganography is proposed in this paper, which can hide a secret digit in a (2^n + x − 1)-ary notational system in a pair of PU partition modes and thus enlarging the capacity. Furthermore, two mapping patterns for PU partition modes are analyzed, and the one that performs the better is selected as the final mapping pattern. Firstly, 8 × 8- and 16 × 16-sized PU partition modes are recorded according to the optimal mapping pattern in the video encoding process. Then, PU partition modes are modified by using the proposed method to satisfy the requirement of secret information. Finally, the stego video can be obtained by re-encoding the video with the modified PU partition modes. Experimental results show that the embedding capacity can be significantly enlarged, and compared with the state-of-the-art work, the proposed method has much larger capacity while keeping high visual quality.

由于高效视频编码（HEVC）是世界范围内流行的视频编码标准，因此HEVC视频的隐写术越来越受到关注。预测单元（PU）是HEVC最重要的创新模块之一；因此，基于PU分区模式的隐写术正成为HEVC隐写术的一个新分支。但是，这种隐写技术的嵌入能力受到PU分区模式类型的限制。为了解决这个问题，本文提出了一种基于改进利用修改方向（EMD）编码的基于PU分区模式的隐写技术，它可以隐藏（2 ^{n  +  x} − 1）-ary注释系统采用一对PU分区模式，从而扩大了容量。此外，分析了用于PU分区模式的两种映射模式，并且选择性能更好的一种作为最终映射模式。首先，在视频编码过程中，根据最佳映射模式记录8×8和16×16尺寸的PU分区模式。然后，通过使用所提出的方法来修改PU划分模式以满足秘密信息的需求。最后，可以通过使用修改后的PU分区模式对视频进行重新编码来获得隐秘视频。实验结果表明，该方法的嵌入能力可以大大提高，并且与最新技术相比，该方法在保持较高视觉质量的同时具有更大的处理能力。