# A Framework for Symmetric-Quality S3D Video Streaming Services
## 2 Related Work  
### Hybrid 3 DTV Utilizing Cross-View SHVC  
HEVC (High Efficiency Video Coding) [16] is a video compression standard designed to maximize compression efficiency, offering approximately 50% better compression compared with the previous AVC (Advanced Video Coding, H.264) standard. This means that high-quality video streams can be delivered with less data transmission. HEVC supports efficient encoding by employing complex prediction models and an irregular tree-based coding unit structure, making it suitable for transmitting high-resolution video content such as 4 K and 8 K at lower bitrates.  
SHVC (Scalable High Efficiency Video Coding) [8] is an extension of HEVC, designed to efficiently encode video streams at various resolutions and quality levels. as shown in Figure 1 SHVC uses a hierarchical structure consisting of a base layer and one or more enhancement layers to flexibly adapt to different network conditions and device capabilities. The base layer contains a lower resolution or lower quality version of the video, while the enhancement layers reference the base layer to progressively improve resolution and quality. For instance, under slow network conditions, only the base layer may be transmitted to ensure minimal quality, and as network conditions improve, enhancement layers can be transmitted to gradually enhance the video quality.  
The main difference between HEVC and SHVC is that SHVC introduces a hierarchical encoding structure that supports scalable video transmission, whereas HEVC focuses on maximizing efficiency through single-layer encoding. SHVC optimizes content delivery across a range of devices, from high-resolution TV displays to mobile streaming services, and adapts to varying network environments to enhance video quality and transmission efficiency. This layered approach provides more flexibility and efficient use of network bandwidth compared with the single encoding method used by HEVC.  
A method has been proposed to deliver 3D video services using the SHVC structure [9]. The method inputs the left- and right-view videos into the base layer and enhancement layer of the SHVC encoder, respectively, as illustrated in Figure 2. By using this method, since the left- and right-view videos are highly correlated with only a difference in viewpoint, it allows for the efficient transmission of both high-resolution and low-resolution videos. This enables 3D video services to be provided without requiring additional bandwidth. We refer to this approach as Cross-View SHVC.  
Figure 2: Cross-View SHVC encoder for the hybrid 3 DTV system.  
Figure 3: Cross-View SHVC decoder for the hybrid 3 DTV system.  
As demand for high-resolution video continues to increase, the high complexity of SHVC has been identified as an issue, leading to ongoing research aimed at reducing its complexity [17; 18]. Cross-View SHVC also faces challenges that require improvements. Figure 4 shows an enhanced version of the structure presented in Figure 2[11]. This improved structure is designed to encode a second enhancement layer while sharing the base layer. The enhanced Cross-View SHVC technique provides, on average, 16% higher encoding efficiency compared with the independent HEVC encoding of the left and right views. Additionally, this method reduces fluctuations in the Peak Signal-to-Noise Ratio (_PSNR_) (1) per video frame and improves the quality of the lowest _PSNR_ frame by 0.6 dB. These improvements enhance bandwidth efficiency as well as the overall quality of 3D video [11].  
\[PSNR=10\log_{10}\frac{R^{2}}{MSE} \tag{1}\]