## 3 Available Techniques to Reduce the Bandwidth of the 360-Degree Video
### Dynamic Adaptive HTTP Streaming (DASH) Framework  
Dynamic adaptive HTTP streaming (DASH) is an MPEG standard that provides a multimedia style and specification for sending material over HTTP using an adjustable \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**VR** & **Resolution** &
\begin{tabular}{c} **Equivalent** \\ **TV Res.** \\ \end{tabular} & **Bandwidth** & **Latency (ms)** \\ \hline \multirow{2}{*}{Early stage VR} & 1K \(\times\) 1K@visual field & \multirow{2}{*}{240P} & \multirow{2}{*}{25 Mbps} & \multirow{2}{*}{40} \\  & 2D\_30 fps\_8 bit\_4K & & & \\ \hline \multirow{2}{*}{Entry level VR} & 2K \(\times\) 2K@visual field & \multirow{2}{*}{SD} & \multirow{2}{*}{100 Mbps} & \multirow{2}{*}{30} \\  & 2D\_30 fps\_8 bit\_8K & & & \\ \hline \multirow{2}{*}{Advanced VR} & 4K \(\times\) 4K@visual field & \multirow{2}{*}{HD} & \multirow{2}{*}{400 Mbps} & \multirow{2}{*}{20} \\  & 2D\_60 fps\_10 bit\_12K & & & \\ \hline \multirow{2}{*}{Extreme VR} & 8K \(\times\) 8K@visual field & \multirow{2}{*}{4K} & \multirow{2}{*}{2.35 Gbps} & \multirow{2}{*}{10} \\  & 3D\_120 fps\_12 bit\_24K & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Network requirement of VR. Figure 2: Bandwidth reduction techniques. bitrate method [21]. DASH is extremely compatible with the existing internet infrastructure due to its minimal processing burden and transparency to middleboxes, and the ability to apply alternative adaption methods makes it adaptable to diverse network conditions standard is generally extensively utilized for two-dimensional video streaming over the world wide web recently. DASH streaming works by splitting videos into short segments, each segment on the DASH server maintains a number of video streams with varying bitrates [19]. By requesting the proper HTTP resource, based on the view on the streaming client, the main viewpoint segment stream with higher resolution and the other viewpoint segment stream with lower resolution. A video player can switch from one quality level to another in the middle of the video playback without interruption. Table 2 demonstrates the major steps in the DASH streaming process:  
Another extension of DASH or other streaming systems is the Omnidirectional Media Format (OMAF) standard specifying the spatial information of video segments [22]. For the DASH OMAF scheme, storage space is sacrificed to increase the bandwidth of the VR video streaming [23]. Figure 3 shows the technical framework of the DASH OMAF architecture network. Furthermore, OMAF specifies several requirements for users, bringing the standard specification for omnidirectional streaming one step closer to completion. Players based on OMAF have already been implemented and demonstrated [24]. OMAF also defines tile-based streaming and Viewport-Based Streaming approaches where the Field of View (FoV) is downloaded at the highest quality possible, along with the lower quality of the other viewable region which will be discussed in detail in the next section. This enables the client to download a collection of tiles with varying encoding qualities or resolutions, with the visible region prioritized to improve the quality of experience (QoE) while consuming less bandwidth. Next, OMAF also specifies video profiles based on the High-Efficiency Video Coding (HEVC) coding standard, as well as HEVC-based or older Advanced Video Coding (AVC), AVC-based viewport-dependent profiles that support Equirectangular Projection (ERP), Cubic Mapping Projection (CMP), and tile-based streaming [25]. The comparison of ERP and CMP is shown in Figure 4.