Content Complexity based Rate Assignment for 360 degree Video Streaming

Master's Thesis from the year 2019 in the subject Computer Science - Applied, grade: 1.7, TU Dortmund (Communication Technology Institute), language: English, abstract: As part of the standardization of new video transmission and coding procedures, new areas of application are moving into focus. An example of these new applications is omnidirectional video, also known as 360-degree video, for viewing through Virtual Reality (VR) glasses. The first specifications for VR services have already been developed by the responsible standardization organizations like the Motion Picture Expert Group (MPEG) and the 3rd Generation Partnership Project (3GPP). In order to supply this high-quality content, the high bandwidth requirement for omnidirectional video contingency became a fundamental problem, since the resolution level can quickly exceed what is available in conventional video applications, especially for mobile content streaming.

One solution is a new transmission approach based on splitting the omnidirectional video into independently coded video tiles of different resolutions. These video tiles are stored on the server-side. During streaming, the client device requests the tiles in the current viewing direction in higher resolution than the tiles outside the field of vision. Complying with the bandwidth capacity of the streaming system is the goal, while the bitrate allocation between tiles shall be such that the corresponding quality distribution between tiles contributes to optimal user experience, i.e. the consistent quality of tiles is the desired outcome of such bitrate allocations. All requested tiles are packed into one constrain compliant video stream and transferred to the client device. For a service provider providing the video data appropriately is a challenge. Video tiles are typically encoded by parallel independent encoder instances.

A proper rate assignment of the total available bandwidth to these instances is, therefore, necessary to achieve a uniform quality across all video tiles. The proprietary implementations of encoders that are in development do not necessarily implement a constant quality mode. Instead, the constant target bitrate (CBR) or rate controlled mode must be used. Finding the proper bitrates which correspond to a uniform quality could be done by a trial-and-error search. However, such an approach comes with an enormous overhead in encoding complexity and is not practicable for newer and computably more complex video encoding standards or on a large scale. Therefore, a rate assignment must be made based on simple complexity features derived from the pictures before encoding.