# DTV Essential Hidden Area Decoder for DTV Broadcasting
## 2 The Conventional DEHA Analysis
### DEHA on MPEG Constant Bitrate (CBR) Encoding  
The MPEG encoding technique is a form of lossy compression that operates on macroblocks, with the last line of macroblocks (LML) consisting of active video and DEHA [18]. In Figure 3, we illustrate the encoding process of the second macroblock within the LML utilizing DEHA. Within this process, the Y21 and Y22 blocks represent the active video region, while the Y23 and Y24 blocks represent the DEHA. The U2 and V2 blocks are divided into the active video and DEHA portions, vertically separated into top and bottom sections. Figure 2: DEHA Magnified DEHA examples of conventional HD broadcasting systems: (**a**) DEHA example for terrestrial DTV broadcasting system; (**b**) DEHA example for internet broadcasting system. Following the transformation of pixel data into frequency components, all coefficients undergo quantization using the macroblock quantization factor (mQuant) and are subsequently encoded using a variable length code. To ensure an even distribution of generated bytes within the video stream, the average number of generated bytes per video frame (B\({}_{\text{frame}}\)) can be calculated using the below equation. \[B_{\text{frame}}=\text{video bitrate / frame rate / 8}. \tag{1}\]  
In a 17.5 Mbps 25 frames/sec video stream, the average generated bytes of the video frame are 87,500 (=17.5 106/25/8) bytes/frame. A video frame is composed of a 68-macroblock line. Thus, the generated bytes of the B\({}_{\text{LML}}\) are as follows:  
\[B_{\text{LML}}=B_{\text{frame}}\ /\ 68. \tag{2}\]  
DEHA is half of the LML. Therefore, the generated bytes of the B\({}_{\text{DEHA}}\) are as follows:  
\[B_{\text{DEHA}}=B_{\text{frame}}\ /\ 136. \tag{3}\]  
There are about 643 bytes per frame for DEHA in a 17.5 Mbps 25 frames/sec MPEG CBR video stream. Consequently, although this is only 0.735%, there are 16.084 Kbytes/sec (128.672 Kbps = B\({}_{\text{DEHA}}\) frame rate) as redundancy in storage or in DTV channel in 17.5 Mbps 25 frames/sec MPEG CBR encoding. In order to analyze the average generated bytes in the last line of macroblocks (LML) with DEHA, we present an example using the CrowdRun sequence from the International Telecommunication Union (ITU)'s video quality test sequences [2]. Figure 4 illustrates the comparison of average generated bytes for different picture encoding types. It is observed that while the generation bytes of Yn3 and Yn4 blocks in the bar mode are lower than those in the reference mode, the generation bytes of Yn1 and Yn2 blocks in the bar mode DEHA are higher [1]. Similarly, the generation bytes of Un and Vn blocks in the bar mode DEHA are also higher compared to the reference mode. Despite the difference in mQuant values, the generation bytes of the LML exhibit minimal variation between DEHA modes, as shown in Figure 4a,b. In 17.5 Mbps, 25 frames per second MPEG CBR encoding, all DEHA modes generate approximately 816 bytes per frame. This corresponds to half the generated bytes in the LML, as depicted in Figure 4a. However, the current utilization of the DEHA is considered redundant in terms of channel utilization and storage efficiency, amounting to 20,400 Kbytes/sec. This discrepancy is attributed to the pixel complexities in the LML, exceeding the theoretical values predicted via Equation (1). In Figure 4b, the maximum difference in bytes per frame between the reference mode and the black bar mode in I-picture is 294.88 bytes, representing a ratio of only 0.146% (=294.88/201,600.2). Despite the variations in generated bytes between DEHA modes, the average generated bytes per frame remain consistently close to 87,500 bytes, as shown in Figure 4b. Figure 3: MPEG video coding sequence of the 2 nd macroblock in the LML with DEHA. Finally, the correlation between the generated bits in bar mode DEHA and reference mode DEHA is depicted in Figure 4c. The correlation coefficient for generated bytes per frame is nearly 1, exceeding 0.99997.