# A Survey on Robust Video Watermarking Algorithms for Copyright Protection
## 5 Robust Watermarking Algorithms Based on Compressed Videos
### H.265-Based Watermarking Algorithms
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref.** & **Type** & **Watermark Preprocessing** & **Embedding Position** \\ \hline
[82] & Blind & CDMA technique & Low-frequency DCT coefficients of Y component of I frames \\ \hline
[83] & Blind & Spread spectrum & Medium–high frequency DCT coefficients of I frames \\ \hline
[84] & Non-blind & Pseudorandom sequence & Highest energy coefficient in 4 \(\times\) 4 luma intra-predicted blocks \\ \hline
[85] & Non-blind & DCT & DCT coefficients of motion coherent blocks in all frames \\ \hline
[86] & Blind & Encryption operation & High-frequency DCT coefficients of all frames \\ \hline
[87] & Blind & Random sequence & L4 \(\times\) 4 type of MBs of I frames \\ \hline
[88] & Blind & Pseudorandom sequence & Index of the reference frame \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary comparison of several H.264-based watermarking algorithms. data hiding and encryption algorithm based on HEVC video. The signs and phases of the motion vector difference and the signs of residual coefficients are encrypted by the key generated by Rivest Cipher 4 (RC4), and the hiding key is used to embed the data into the nonzero AC residual coefficients. In a past paper [100], a HEVC-based watermarking algorithm with high payload was proposed, and the watermark was embedded into quantized transform coefficients (QTCs) during the encoding phase. Based on all phase biorthogonal transform (APBT) and SVD, [PERSON] et al. [101] proposed a video watermarking algorithm against HEVC recompression. In the watermark preprocessing process, the watermark is compressed by APBT, which increases the embedding capacity by more than three times. Aiming at the HEVC coding process, [PERSON] and [PERSON] [102] proposed an efficient information hiding algorithm based on motion vector space coding. The mapping relationship between the motion vector set and points in the motion vector space is defined first, and the secret information is embedded into the motion vectors of the smallest PUs in coding tree unit (CTU). [PERSON] [103] proposed a new information embedding scheme based on modifying split decisions of HEVC video. At the encoding phase, the mapping relationship between split decisions of the coding unit (CU) and its characteristic variables is calculated to generate model weights that can be used to predict the split decisions, and then the message is embedded according to the prediction and real split decisions of each CU. The summary comparison of several watermarking algorithms based on H.265 is shown in Table 11.  
In addition, to help readers know the performance of compressed video-based algorithms involved in the paper quickly, Table 12 gives the quantitative comparison of invisibility, capacity, BIR, and robustness of several typical algorithms in compressed domain. In Table 12, the numbers in \"()\" indicate the parameters of attacks and \"-\" shows that the attack is not mentioned in the reference. The reason may be that the algorithm cannot resist the attack, or the authors have not considered it. The full names of several typical attacks corresponding to the abbreviations mentioned in Table 12 are given in Table 1.