# A Survey on Robust Video Watermarking Algorithms for Copyright Protection
## 1 Introduction  
The digitization of multimedia information, along with the development of computer technology and networks, has brought great convenience to the generation, storage, and dissemination of digital products, such as images, audios, and videos. Especially, network bandwidth and computer storage capacity have been greatly improved under the influence of Moore's law [1]. Meanwhile, with the widespread popularity of the Internet, the exchange of multimedia information has penetrated into every corner of social life. In recent years, webcast and video-on-demand (VOD) services have begun to rise and spread rapidly around the world, and the developments of the film and TV show industries are booming. As a result, the number and duration of online videos are increasing explosively, and the content is all-encompassing. Through the Internet, people can copy, process, and transmit videos of interest at will, which brings great convenience to people. However, it is followed by illegal acts such as piracy, infringement, and stealing, which not only damage the intellectual property rights of digital works' owners, but also affect the market order of electronic publications. Additionally, pirated works may pose a great threat to the safety of users because they are of poor quality and may carry and spread computer viruses. The issue of piracy infringement is undoubtedly a huge obstacle to the healthy development of the video industry. Therefore, copyright protection for digital video is extremely urgent [2]. The conventional copyright protection technology is cryptography [3], which guarantees the security of digital products through a secret key. Whether the important information is processed by a symmetric key system or a public key system with higher security, the obtained data are all garbled,so in the transmission process, attackers can only see these garbled codes and cannot decipher the confidential information, thus they cannot pirate. However, if the code transmitted between the two sides of the communication always seems to be meaningless, it may easily attract the attention and interest of attackers and then become the target. Once the cipher text is cracked, the encrypted data will become easily available. In addition, the copyright owner cannot monitor the files decrypted by legal users. As a result, the protection of encrypted data becomes ineffective and intellectual property rights cannot be traced and confirmed. Under this background, information hiding technology [4] with camouflage characteristics has emerged as these times require. Information hiding technology hides important information in another open digital product, and then confidential information is transmitted by delivering the open carrier, which is an effective method to realize the secure transmission of confidential information in the network [5; 6]. Information hiding technology mainly includes steganography [7], digital watermark [8], and covert communication [9], and its main branches are shown in Figure 1.  
Among these technologies, digital watermark, an important branch of information hiding, can truly solve the problem of copyright protection for digital products. It embeds invisible signs into digital products such as copyright information or authentication information. In this way, unauthorized users cannot detect the hidden information, and copyright protection can be achieved. When pirated products appear, product owners can extract hidden information to prove the copyright ownership and trace the acts of infringement. Besides, they can also provide legal evidence for charging illegal infringement. The original purpose of digital watermarking technology is to protect copyright. With the development of the technology, its application scope has become more and more extensive, including copyright protection, copy control, fingerprint identification, content authentication, broadcast monitoring, video tracking, and so on [10].