Existing multimodal recommenders largely rely on late fusion, where modalities are separately encoded and aligned before fusion. Such designs work well with complete content but become fragile in practice: modalities are often missing, alignment breaks down, and imputation adds complexity with limited benefit. We propose EFMRec, a missing-aware early-fusion framework that follows a relaxed principle of leveraging modalities when available and ignoring them when absent. By exploiting pretrained multimodal models, EFMRec projects available modalities into a shared semantic space and aggregates them through a missing-aware early fusion, producing unified representations without reconstruction or auxiliary losses. These representations are further propagated via a GCN-based architecture and integrated with a collaborative filtering backbone to jointly model multimodal and collaborative signals. Experiments on three benchmarks demonstrate that EFMRec consistently outperforms strong baselines under both full- and missing-modality settings, highlighting its robustness to modality incompleteness.

The Visual Security Index (VSI) of encrypted videos measure the security of encryption algorithms by evaluating the visual information content, which provides a critical evaluation criterion for selective encryption. The VSI for encrypted videos needs to assess security in both spatial and temporal domains. Existing visual security metrics, which rely on averaging, optical flow, and convolutions, fail to capture information leakage in the temporal domain effectively. This paper proposes a spatiotemporal self-attention-based video security assessment model called Spatiotemporal Self Attention (StSA). In the spatial domain, windowed self-attention is used to calculate regional correlations within video frames. By introducing multi-layer outputs, a multi-depth self-attention network named Multi-Depth Swin-Transformer (MDST) is constructed to compute the regional correlation within video frames. A weak label calculation method based on edge similarity is proposed to calculate the scores for frames and blocks based on the video Mean Opinion Score (MOS), thereby supporting the pre-training of spatial models. In the temporal domain, considering human visual persistence characteristics and the one-way relationship between video frames, temporal unidirectional window self-attention is proposed to calculate frame correlations in the temporal sequence. Finally, the visual security index score for encrypted videos is obtained by combining the spatiotemporal correlation changes of encrypted and plaintext videos. Experimental results show that StSA achieves a Pearson Linear Correlation Coefficient (PLCC) of 0.955 and a Root Mean Squared Error (RMSE) of 0.458 on the encryption datasets. Compared to other visual security metrics, StSA demonstrates higher accuracy and correlation, effectively capturing spatiotemporal information leakage in encrypted videos and reflecting the human perception of the security.

The security protection of Ultra-High-Definition (UHD) video is facing grand challenges due to changeable application scenarios. The video business is highly dependent on the video format structure, which makes the format compliance of the encryption algorithm essential. Existing HEVC Selective Encryption (SE) algorithms are difficult to encrypt with format compliance while independent from the encoding, which limits their practical application. In order to realize the format compliant encryption on encoded bitstream, this paper first proposes a non-diffusion rule by analyzing the coding format specification of High Efficiency Video Coding (HEVC). Following the non-diffusion rule, a Bit Flipping (BF) method and a Bit Insertion-Deletion (BID) method are proposed based on the lower bound mapping of the bypass syntax element bit coding interval. Then, considering the various binarization methods and the correlation between syntax elements when decoding, this paper proposes the Validity Principle (VP) and Independence Principle (IP) of format compliant encryption. Focusing on the binary bits of the primary bypass elements in HEVC, the encryptability of them is analyzed in detail, and the corresponding format compliant encryption schemes based on BF, BID methods are constructed. Based on the above, a Format Compliance Encryption (FCE) framework after encoding is formulated. The flexibility, security, and adaptability of the framework are analyzed. Finally, through experiments from the aspects of format compliance, encryption speed, and perception effect, the proposed methods, schemes, and framework are format compliance while ensuring the basic performance and security requirements.