# A Survey on Robust Video Watermarking Algorithms for Copyright Protection
## 4 Robust Watermarking Algorithms Based on Original Videos
### Video Watermarking in Transform Domain
#### 4.2.1 DCT-Based Watermarking Algorithms  
Due to the energy compaction characteristic of DCT, the energy of video frames after DCT transform is mainly concentrated in DC coefficients and low-frequency sub-band [33]. Compared with the high-frequency sub-band, the human eye perception and robustness are better in the low-frequency sub-band. Therefore, the selection of watermark embedding positions should consider the compromise between invisibility and robustness. [PERSON] et al. [34] proposed a robust video watermarking algorithm in DCT domain based on high-frequency coefficients correlation algorithm. To prevent high-definition (HD) videos from unauthorized copying, [PERSON] et al. [35] proposed a recoverable video watermarking algorithm in DCT domain based on code division multiple access (CDMA) modulation. [PERSON] and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref.** & **Type** & **Watermark Preprocessing** & **Embedding Position** \\ \hline
[26] & Blind & Encoding &
\begin{tabular}{c} MDSB of Y component, \\ LSB of U and V components \\ \end{tabular} \\ \hline
[28] & Blind & Pseudonoise sequence & Each frame \\ \hline
[29] & Blind & Pseudorandom noise generator & Luminance component of each frame \\ \hline
[30] & Blind & - & Luminance component of each frame \\ \hline
[31] & Semi-blind & - & Blocks with robustness to most attacks \\ \hline
[32] & Blind & Arnold transform & Frames selected by scene change \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary comparison of several watermarking algorithms in spatial domain. [PERSON] [36] embedded eight bit-plane images decomposed from a grayscale watermark image into DCT coefficients with robustness, which were selected in the video luminance component using an even-odd quantization algorithm. In a previous paper [37], selected regions, based on the properties of the human visual system (HVS), were converted to the YUV space, and then the Y component was processed to extract Krawtchouk moments using optimal orders which can maximize the quality of the reconstruction. The DCT scheme is implemented to the obtained Krawtchouk moments to achieve the embedding process combining the secret key. [PERSON] et al. [38] adopted the KAZE feature to achieve the synchronization between the watermark embedding and extracting regions in the video watermarking algorithm. The KAZE feature points are extracted from a video frame, and matched with those of frame-patch to detect the embedding and extracting regions in all frames. The watermark is inserted into randomly generated blocks in matched regions in DCT domain. What is more, the quantization index modulation (QIM) [39] scheme is adopted in many DCT-based watermarking algorithms [40; 41; 42; 43]. In another past paper [40], to reduce computation time, a pseudo-3D DCT transform by two times of DCT transform was introduced. By adjusting the correlation between DCT coefficients of selected blocks, the watermark is embedded into continuous video frames converted into pseudo codes before compression combining the QIM scheme. While embedding the watermark, some information is recorded as a secret key to strengthen the security of the algorithm. [PERSON] et al. [41] combined QIM with pseudo-3D DCT and proposed a blind video watermarking algorithm. Pseudo-3D DCT is used to obtain the embedding factor and useful messages. The watermark is embedded into the luminance component of each I frame in original video based on the correlation between DCT coefficients. The use of QIM makes it easy to derive the embedding position of the watermark. However, this algorithm cannot resist geometric attacks, like scaling. Combining the spatial and temporal dimensions of video sequences, [PERSON] and [PERSON] [42] proposed a watermark embedding technique based on QIM and rational dither modulation (RDM). The video is divided into spatial and temporal dimensions, and projected into the 3D DCT domain. Then, a set of transform coefficients are selected according to the rules for watermark embedding, [PERSON] et al.