Design And Implementation Of Low Latency H.265-based Video Transmission System

In recent years,with the development of IC(integrated circuit)industry and embedded tech-nology,UAV(Unmanned Aerial Vehicle)technology has step into the rapid development stage.At the same time,the demand for high-quality UAV video transmission system has become ever more urgent.Image is one of the most important information captured by the UAV.In order to realize the precise control of the UAV,it is necessary for the video trans-mission system to satisfy various requirements such as high video quality,small network bandwidth occupation,low latency and high reliability.Video codec latency time is the most important component among video transmission system latency.Therefore,on the premise of high video quality with limited network bandwidth,it is of great practical significance to reduce video coding and decoding latency.H.265 has the advantages of high compres-sion ratio and easy parallelization of coding structure,which is very suitable for UAV video transmission system application.A low latency video transmission system is designed based on H.265 in this paper.The video transmission system has excellent characteristics in high versatility and high robustness,and can provide low latency HD video transmission service for UAVs.Firstly,the encoding terminal is designed based on the HiSilicon HI3516 and makes full use of the H.265 encoder on HI3516.The encoding terminal has the functions including the video capture,encoding and transmission.The decrease of network efficiency due to the fluctuation of H265 stream can be improved by P-frame intra-frame refresh technology.And then,software operation is efficiently improved by adopting multi-threading technology and optimizing software structure.Secondly,the decoding terminal is designed based on the Rockchip RK3288,which has the functions including the network data reception,H.265 decoding and video display.Efficient H.265 decoding is achieved by calling the Rockchip MPI and rational allocating buffers.Im-age rendering is performed using DRM,and DMA-BUF technology is used to realize zero copy of image display.The raw socket is applied to improve the network transmission effi-ciency.The memory mapping technology is employed to reduce the number of the network data copies,thereby effectively reducing the network data receiving time.Finally,the video transmission system is built with professional camera and monitor,and it is tested both in laboratory and airborne environment using a LAN or WAN as transmission medium.The test results show that the system is capable of encoding 1080P@60FPS quality video and transmitting it at 4Mbps stream rate.The end-to-end latency is 150ms in the LAN,and the encoding terminal power is less than 3W.Multiple experiments show that the video transmission system is complete in function,excellent performance and extremely robust.