## 4 Panoramic Live Broadcast  
### Steps to Implement Panoramic Live Broadcast  
In October 2015, the standardization of the panoramic video packaging format was launched by MPEG, called omnidirectional media format (OMAF) [36], which was jointly developed by experts from high-tech enterprises, research institutions, and universities around the world. It is stipulated in the OMAF standard that a panoramic video spliced on the server side can be streamed using a DASH or MPEG media transport protocol after content preprocessing, encoding, and encapsulation. On the one hand, an OMAF player can receive, parse, and present relevant media content; on the other hand, it needs to track a user's head movements, eye movements, and other interactive operations to feed back window information in real time. Figure 1 shows the panorama video processing flow specified in the OMAF standard. Shooting and splicing: A panoramic camera is required to obtain panoramic videos, whose information is sourced from a composite of multiple cameras. In cases where a higher video resolution is required, more cameras of higher resolution are needed. Stitching technology is used to place the pictures of all cameras around the observer to generate the panoramic picture. If there are six ideal identical cameras, they should be placed on a bracket with a strict position and rotation to take pictures in four horizontal directions and in the up and down directions; thus, pictures that are taken should be spliced together to form a square. In that case, the results can be used directly without optimization. However, it can be difficult and even impossible to accurately meet the above standards. Therefore, some researchers use methods [37] to reserve image redundancy and correctly identify and process the areas where the images of two cameras overlap and then splice them. Projection and back projection: Each frame of a panoramic video is presented in the form of a sphere. However, the original video coding standards are applied to the transmission of panoramic video. That means there should be preprocessing before transmission. The process of mapping the spliced picture to a rectangular picture is called projection. At present, the OMAF standard only supports longitude and latitude maps, equirectangular projection (ERP), and cube mapping (CMP) [36]. ERP is similar to the generation of the world map. In ERP, people look from the center of the sphere outward to the surface of the sphere inward, while for the world map, they look at the sphere from the outside to the inside. In CMP, the complete sphere is divided into six regions, which are projected onto each of the six faces of the cube. The bottom, back, and top faces need to be arranged together with the other three faces to form a rectangular frame through a specific rotation operation. In order to improve the coding efficiency, the operation principle of the three rotating surfaces is to maintain the consistency of the media content at the junction of the arrangement time surface and the surface [36]. Encoding and decoding: Traditional video encoding and decoding schemes may meet the codec requirements of panoramic video streams. However, because panoramic video itself is different from traditional video, many problems arise when traditional schemes are applied to panoramic video, such as geometric distortion, discontinuous pictures, etc. As a result, various optimization schemes for panoramic video codecs have been put into practice [38; 39]. Streaming: It was described in the second part of the related work that there were three mainstream panoramic live broadcast schemes: full-view video streaming, viewport-based video streaming, and tile-based video streaming. Determining how to make a better choice between improving video quality and reducing transmission bandwidth is still the main direction of current and future research. Figure 1: The OMAF architecture for panorama video processing flow. Three main steps are involved: content authoring, delivery, and playing.