## 2 Related Works  
Video steganography systems can be classified into three main classes, namely still picture steganography, metadata methods, and raw video techniques [9; 10]. The still picture steganography views video steganography as an extension of image steganography. Since a video segment is composed of sequential still images, still picture steganography methods are based on embedding the confidential data frame by frame independently. Still picture steganography can be subdivided into native domain technique, and frequency domain techniques. The least-significant-bit (LSB) techniques are the most classical approaches in steganography. The LSB technique hides the secret data in the least significant bit planes of the frames of the video segment. LSB techniques are favorable due to their simplicity and low computational complexity. However, it has been widely known that data hidden using simple LSB substitution techniques can be easily discovered using basic steganalysis methods [11]. Therefore, recent LSB techniques are usually integrated with other techniques to strengthen the steganography system. A video LSB-based technique is proposed in [12]. The proposed technique aimed to improve the LSB performance by integrating the basic LSB technique with the genetic algorithm (GA). This proposed LSB-GA technique was able to achieve an enhanced quality of the carrier video signal when hiding at a similar rate to basic LSB techniques. The carrier quality reached up to 39.37 dB while hiding with an average of 2.66 bits per gray-scale pixel. Another video LSB-based method is presented in [13]. This proposed method used only one LSB plane for each frame from the host segment for hiding. As a result, this technique was able to achieve a high imperceptibility level since only one LSB is utilized for hiding. However, the embedding rate is low compared to other steganography systems in the literature. The tri-way pixel-value differencing (TPVD) is another spatial domain technique [14]. The tri-way pixel-value differencing (TPVD) technique is based on the popular pixel-value differencing (PVD) technique. The PVD technique hides the confidential data in the difference value of two adjacent pixels. A TPVD-based video steganography technique is proposed in [15]. The proposed technique adopted the TPVD algorithm to hide in a compressed domain of the host video segment. The other subclass under the still pictures method is the frequency-domain method. These techniques convert the host frames from their native spatial domain into a domain that facilitates frequency analysis. The transform can be done using one of the frequency analysis tools such as the discrete Fourier transform (DFT), discrete cosine transform (DCT), and discrete wavelet transform (DWT). The confidential data are then hidden by replacing some selected frequency coefficients with the secret data. A DWT-based technique is presented in [16]. This proposed technique used the Bose-Chaudhuri-Hocquenghem (BCH) codes to encode the secret bits and then hide them in the DWT coefficients of the video frames. The proposed technique embedded the confidential data in all DWT coefficients excluding the low-frequency DWT coefficients. The reason is that low-frequency coefficients contain the most critical parts of the signal, which must remain intact to maintain an acceptable quality of the carrier frame. The proposed technique achieved a higher hiding rate compared to similar approaches in the literature. Another DWT scheme was proposed in [17]. This DWT technique is a blind scheme where embedding is performed in human skin regions in a frame. Hiding is done in the blue and red channels using a wavelet quantization method. The proposed scheme was tested against MPEG-4 compression and showed a good robustness level. The second class is the metadata schemes. These schemes target a specific video format by exploiting the structure and the compression algorithm adopted in the format. An example of a popular standard video format is the H.264/AVC format.