ROI (Region of Interest) video selective encryption based on H.265/HEVC is a technology that protects the sensitive regions of videos by perturbing the syntax elements associated with target areas. However, existing methods typically adopt Tile (with a relatively large size) as the minimum encryption unit, which suffers from problems such as inaccurate encryption regions and low encryption precision. This low-precision encryption makes them difficult to apply in sensitive fields such as medicine, military, and remote sensing. In order to address the aforementioned problem, this paper proposes a fine-grained ROI video selective encryption algorithm based on Coding Units (CUs) and prompt segmentation. First, to achieve a more precise ROI acquisition, we present a novel ROI mapping approach based on prompt segmentation. This approach enables precise mapping of ROIs to small $8\times8$ CU levels, significantly enhancing the precision of encrypted regions. Second, we propose a selective encryption scheme based on multiple syntax elements, which distorts syntax elements within high-precision ROI to effectively safeguard ROI security. Finally, we design a diffusion isolation based on Pulse Code Modulation (PCM) mode and MV restriction, applying PCM mode and MV restriction strategy to the affected CU to address encryption diffusion during prediction. The above three strategies break the inherent mechanism of using Tiles in existing ROI encryption and push the fine-grained level of ROI video encryption to the minimum $8\times8$ CU precision. The experimental results demonstrate that the proposed algorithm can accurately segment ROI regions, effectively perturb pixels within these regions, and eliminate the diffusion artifacts introduced by encryption. The method exhibits great potential for application in medical imaging, military surveillance, and remote areas.

翻译：基于H.265/HEVC的ROI（感兴趣区域）视频选择性加密是一种通过扰动目标区域相关语法元素来保护视频敏感区域的技术。然而，现有方法通常采用Tile（尺寸较大）作为最小加密单元，存在加密区域不精确、加密精度低等问题。这种低精度加密使其难以应用于医疗、军事和遥感等敏感领域。为解决上述问题，本文提出一种基于编码单元（CU）与即时分割的细粒度ROI视频选择性加密算法。首先，为获取更精确的ROI，我们提出一种基于即时分割的新型ROI映射方法。该方法能够将ROI精确映射至较小的$8\times8$CU级别，显著提升加密区域的精度。其次，我们提出一种基于多语法元素的选择性加密方案，通过扰动高精度ROI内的语法元素来有效保障ROI安全。最后，我们设计基于脉冲编码调制（PCM）模式与运动矢量（MV）限制的扩散隔离机制，对受影响的CU应用PCM模式与MV限制策略，以解决预测过程中的加密扩散问题。上述三种策略突破了现有ROI加密中依赖Tile的固有机制，将ROI视频加密的细粒度推至最小$8\times8$CU精度。实验结果表明，所提算法能够精确分割ROI区域，有效扰动区域内像素，并消除加密引入的扩散伪影。该方法在医学影像、军事监控及偏远地区等领域展现出巨大应用潜力。