# A Novel Video Transmission Latency Measurement Method for Intelligent Cloud Computing
## 1 Introduction  
With the rapid development of cloud based real-time AI, network video services are now available for interactive applications requiring a closed loop response [1]. Cloud VR and autonomous systems, including drones, vehicles, and robots, can achieve the same level of performance at fraction of the cost through cloud processing. Vehicles that can carry advanced accident detection systems, micro drones navigating through complex forests at high speeds, VR users with light weight googles without suffering dizziness, robots that recover from trips; all these applications require reliable low latency delivery of content to and from the cloud. One critical content component is video. Different video applications require different video transmission latencies to ensure QoS (quality of service). One-way video transmission applications such as live video and VOD (video on-demand) only require a latency within 2-5 s [2]. Interactive video applications such as video conference have become more and more popular. The latency of video software such as Zoom is between 300 ms and 1 s [3]. For emerging applications such as cloud based real-time AI control, VR, and cloud games that require high interactivity, the latency is required to be less than 20 ms in order maintain control over these vehicles in their dynamic environments, or to avoid users' feelings of vertigo during use [4]. With the rise of new applications, people's requirements for real-time video are also increasing. The transmission mode of video applications has gradually developed from one-way video transmission to interactive video transmission. In order to guarantee the QoS of video latency in interactive video scenes, it is necessary to monitor the video transmission delay of each application in real time and online. There exists a significant amount redundancy in raw digitized video, including spatial redundancy, temporal redundancy, and coding redundancy. In order to ensure the efficient remote transmission of video, it is necessary to apply video compression technology tothe video transmission process. This paper defines a video transmission system with five processing stages:  
* Capture
* Compression
* Transmission
* Decompression
* Display  
Each stage will bring its corresponding latency. 1. Capture  
Almost all cameras in the market have a certain latency between capturing and outputting video information. [PERSON] et al. [5] proposed a method to measure the latency of cameras and tested a series of cameras. The measurement results show that the latency generated by the Blackmagic URSA Mini Pro 4.6 K (for South Melbourne, Victoria, Australia) is the smallest, between 4 and 8 ms, whereas most of the camera latencies are at range between 1 and 3 video frames. 2. Compression/Decompression  
The latency introduced by video compression and decompression is related to the complexity of video encoding and decoding algorithms. Following the processing complexity, video compression can be divided into two types: light-weight compression and hybrid compression. Light-weight compression is mainly based on image coding. For example, Apple ProRes is a variable bit rate video codec that can independently encode and decode each video frame with a compression ratio between 4 and 6 for real-time video editing [6; 7]. TICO is a codec that uses only intra-frame compression with a compression ratio of 4:1; this is used in the 4K UHD TV industry [8]. JPEG-XS is a lightweight codec, which can achieve a compression ratio of 6:1 and is used in applications within the live broadcast and the AR/VR systems [9; 10; 11] space. Light-weight compression is mostly used in professional fields. Although the compression ratio is small, the latency is greatly reduced. Due to limited bandwidth, videos on the internet are usually transmitted after hybrid compression, with a compression ratio in the range of 250-500 [12; 13; 14]. The current international mainstream video coding standards include H.264/AVC, H.265/HEVC, H.266/VVC, AVS [15], and VP9/AV1 [16].