| The rapid development of wireless communication and intelligent mobile phone technology makes HD video surveillance system possible. Most of the existing mobile video surveillance system can only transmit low bit rate (300Kbit/s) SD video (CIF format). To improve the quality of video, this paper designs a 4G mobile HD video surveillance system based on a variety of network and video key technologies, and It can transmit high bit rate (1Mbit/s)HD video (D1、720P、1080P) stably.This paper describes the overall system scheme, and focuses on implementation of video acquisition transmission platform software and Android monitoring client software. For the video acquisition transmission platform software, a dual thread single buffer mechanism is applied to solve the data flow oscillation caused by network jitter. With conditional variables and mutex locks, multithreading synchronization is implemented to schedule tasks. For the Android client software, this paper imports Android percentage layout library for UI layout, improving the UI compatibility of different screen size. And re-implement translation animation with AsyncTask in case of the UI thread blocking. This paper embeds VLC for Android to implement video playing function. In order to solve video decoding error caused by network packet loss and network delay, it proposes a video frame data buffering and verifying mechanism. The mechanism filters incomplete video frames through buffering a whole frame and verifying it’s integrity, and it eliminates the decoding error as well as optimize the video playback effect.Mobile HD video surveillance system transmits data through wired and wireless hybrid network. Due to TCP’s transmission delay and UDP’s packet loss in wireless network, this paper uses UDT protocol for video transmission. For the UDT protocol existing network congestion decision mechanism does not distinguish wireless error packet loss and packet loss caused by congestion, this paper proposes a RTT-based (Round Trip Time) network congestion judgment strategy. This strategy determines the network congestion combining with RTT and packet loss, and it’s added to the UDT to be BRC-UDT protocol. This paper tests TCP, UDT and BRC-UDT protocol in WIFI LAN and 4G network. The experiment results show that the BRC-UDT protocol has a significant improvement in the transmission rate compared to the TCP and UDT.After the implementation of the whole system, a system prototype is developed, and the system prototype is tested in real network. Test results show that the 4G mobile HD video surveillance system transmits video clearly, and it is stable and practical, it can meet the actual needs. |
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