## 2 Related Work
Context-adaptive binary arithmetic coding (CABAC) and context-adaptive variable-length coding (CAVLC), two H.264 codec entropy coders, were discussed to examine the comparative effect of channel errors on selectively encrypted videos in [26]. They concluded that CAVLC was more susceptible to channel errors than CABAC in analyzing the combined effect of selective encryption and compression on video quality. Since all advanced and hybrid encoders support CABAC, this entropy encoder was selected for developing the proposed error correction technique in our work. A selective encryption method for H.264/AVC videos based on CABAC is presented in [27], involving zig-zag scanning followed by encryption of discrete cosine transform (DCT) coefficients, which significantly impacts the texture and content of videos during compression. The scrambling process efficiently provides confidentiality by rearranging macroblocks (MB) of data in a way that makes unauthorized access difficult. An H.264/AVC syntax-based selective encryption method utilizing multiple syntax elements, such as residual coefficients (RCs), transform coefficients (TCs), and motion vectors (MVs), to scramble video contents is presented in [28]. Another selective encryption scheme using the CABAC encoder for VVC is proposed, which identifies TCs, MVs, intra-prediction, and inter-prediction modes as sensitive syntax elements. This scheme encodes syntax elements and selects encoded bins for encryption, which are then encrypted using a symmetric-key encryption algorithm [16]. Selective encryption schemes can be categorized as syntax element-based, bitstream-based, and hybrid encryption. Syntax element-based encryption encrypts specific syntax elements; bitstream-based approaches encrypt the entire bitstream, including syntax and non-syntax elements; whereas hybrid approaches combine both of them to provide robust security. An H.265/HEVC-based hybrid scheme of symmetric-key selective encryption was proposed using the CABAC encoder, which targets sensitive syntax elements including the transform unit (TU), motion vector differences (MVDs), intra-prediction modes (IPMs), inter-prediction modes (InterPMs), and coding unit (CU) flags. The quality of encrypted frames is evaluated through PSNR and SSIM [29]. In [30], the authors proposed AES-CTR encryption built upon an improved CABAC algorithm to selectively encrypt syntax elements, including the suffixes of sign bits, absolute values of residuals of MVDs, DCT coefficients, and QPs. Their proposed approach encrypts specific parts of the video, ensuring sufficient protection from unauthorized access while maintaining format compliance, thus achieving a balance between security and efficiency, making it suitable for real-time applications. Similarly, a 4D hyperchaotic algorithm using the CFB mode of AES is implemented in [31] for privacy protection of videos based on different syntax elements (IPM, MVD, residual coefficients, and delta QPs). PSNR and SSIM reference indicators are used to measure the perceived effect of the video. A selective encryption scheme for H.264/AVC video content is proposed in [32], encrypting only critical parts such as IPMs, MVDs, and RCs. It balances security and efficiency and ensures format compliance utilizing the chaos-based approach to offer reduced computational overhead. However, its security is dependent on the chaotic system and requires careful consideration of key management and security threats. In [33], the authors review existing selective encryption schemes in HEVC and suggest a selective encryption method that generates encrypted bitstreams, records syntax elements, and reconstructs original elements to design a pseudo-key stream for decryption. Experimental analysis is conducted across various QPs to assess the effectiveness of the scheme. The authors in [34] present a secure and efficient data hiding method in encrypted H.264/AVC bitstreams, using IPMs and MVDs to protect information related to texture and motion. An additional security layer is achieved through RCs.