# Multi-Stream Switching for Interactive Virtual Reality Video Streaming

## TL;DR

This paper introduces a multi-stream switching framework for VR video streaming that enhances quality by dynamically selecting pre-encoded streams based on user head movement, optimizing for bandwidth and latency constraints.

## Contribution

It proposes a novel optimization framework and algorithm for multi-stream VR video switching that improves streaming quality over traditional single-stream methods.

## Key findings

- Up to 2.9dB PSNR improvement over non-switching approaches
- Optimization effectively balances bandwidth, storage, and distortion
- Dynamic stream switching enhances VR viewing experience

## Abstract

Virtual reality (VR) video provides an immersive 360 viewing experience to a user wearing a head-mounted display: as the user rotates his head, correspondingly different fields-of-view (FoV) of the 360 video are rendered for observation. Transmitting the entire 360 video in high quality over bandwidth-constrained networks from server to client for real-time playback is challenging. In this paper we propose a multi-stream switching framework for VR video streaming: the server pre-encodes a set of VR video streams covering different view ranges that account for server-client round trip time (RTT) delay, and during streaming the server transmits and switches streams according to a user's detected head rotation angle. For a given RTT, we formulate an optimization to seek multiple VR streams of different view ranges and the head-angle-to-stream mapping function simultaneously, in order to minimize the expected distortion subject to bandwidth and storage constraints. We propose an alternating algorithm that, at each iteration, computes the optimal streams while keeping the mapping function fixed and vice versa. Experiments show that for the same bandwidth, our multi-stream switching scheme outperforms a non-switching single-stream approach by up to 2.9dB in PSNR.