  Over the past decade, the utilization of UAVs has witnessed significant
growth, owing to their agility, rapid deployment, and maneuverability. In
particular, the use of UAV-mounted 360-degree cameras to capture
omnidirectional videos has enabled truly immersive viewing experiences with up
to 6DoF. However, achieving this immersive experience necessitates encoding
omnidirectional videos in high resolution, leading to increased bitrates.
Consequently, new challenges arise in terms of latency, throughput, perceived
quality, and energy consumption for real-time streaming of such content. This
paper presents a comprehensive survey of research efforts in UAV-based
immersive video streaming, benchmarks popular video encoding schemes, and
identifies open research challenges. Initially, we review the literature on
360-degree video coding, packaging, and streaming, with a particular focus on
standardization efforts to ensure interoperability of immersive video streaming
devices and services. Subsequently, we provide a comprehensive review of
research efforts focused on optimizing video streaming for timevarying UAV
wireless channels. Additionally, we introduce a high resolution 360-degree
video dataset captured from UAVs under different flying conditions. This
dataset facilitates the evaluation of complexity and coding efficiency of
software and hardware video encoders based on popular video coding standards
and formats, including AVC/H.264, HEVC/H.265, VVC/H.266, VP9, and AV1. Our
results demonstrate that HEVC achieves the best trade-off between coding
efficiency and complexity through its hardware implementation, while AV1 format
excels in coding efficiency through its software implementation, specifically
using the libsvt-av1 encoder. Furthermore, we present a real testbed showcasing
360-degree video streaming over a UAV, enabling remote control of the drone via
a 5G cellular network.
