# A Framework for Symmetric-Quality S3D Video Streaming Services
## 1 Introduction  
Three-dimensional video services have a long history, with their roots primarily in the film industry. Since the early 20 th century, 3D films have evolved as a technology that displays two images from different angles simultaneously, providing audiences with a sense of depth and immersion. Early 3D films relied on simple analog technology, using two projectors to create a stereoscopic effect, offering viewers a new visual experience. However, due to technological limitations and high costs at the time, 3D films were not widely popular and were mostly reserved for special events or limited screenings. In the 1950s, the first boom of 3D video services occurred, but it faded due to technical challenges and the complexities of the viewing environment. By the 1980s, the introduction of large-format films like IMAX brought renewed attention to 3D technology, offering audiences a more immersive viewing experience. However, many viewers experienced eye strain and discomfort during 3D viewing, limiting its widespread adoption. In the late 2000s, advancements in digital technology led to a resurgence of 3D video service [1]. The release of Avatar in 2009 marked a turning point, prompting the production of more 3D content and the upgrade of theaters with digital equipment for 3D screenings. Despite this, public interest in 3D video services gradually waned due to the inconvenience of wearing 3D glasses, the limited availability of 3D content, and the eye strain experienced by some viewers. Additionally, the perception that the difference in immersion between 3D and 2D formats was not significant led many to prefer 2D videos. Consequently, while 3D video services enjoyed a period of popularity, they eventually fell out of favor as they were perceived to lack sufficient distinction from 2D formats. However, 3D technology is now exploring new possibilities beyond the film industry by merging with emerging technologies such as VR (virtual reality) and AR (augmented reality). VR and AR are technologies that maximize immersion and interactivity, and when combined with 3D video services, their potential can be greatly amplified. In line with this trend, research and development in 3D technology are actively progressing, opening new possibilities in various application fields [2; 3; 4]. To provide hyper-realistic video services utilizing VR and AR, two separate video streams are required, which demand significant computational power and bandwidth. In other words, to deliver a 3D video service, two separate video streams, one for each eye, must be received and combined to create a 3D image [5]. This process requires high-definition video to be received through two channels, which doubles the bandwidth needed compared with traditional 2D video. Receiving two high-definition video streams within the constraints of limited bandwidth and combining them into a 3D image has been a significant technical challenge. To address this bandwidth issue, a hybrid 3 DTV system was proposed [6]. The hybrid 3 DTV system is fully compatible with existing broadcasting systems and uses a method that combines high-definition DTV video with mobile-resolution video for the left and right images to create a 3D video. This allows for the delivery of 3D services without additional bandwidth consumption and has been standardized by the ATSC (Advanced Television Systems Committee) under the name SC-MMH (Service Compatible-Main and Mobile Hybrid Delivery) [7]. This system is an innovative technology that provides 3D services while maintaining compatibility with existing 2D-HD or -UHD broadcasts, and it is designed to simultaneously offer mobile SD, terrestrial HD, and stereoscopic 3D services in various user environments. As a result, users can enjoy an optimal 3D viewing experience on a range of devices, from mobile devices to large displays. Moreover, it has the advantage of providing 3D video and broadband services by utilizing existing 2D-HD (right view) and 2D-UHD (left view) broadcasts without the need for additional equipment.