Abstract: A method based on H. 264 mobile video surveillance system, using i. As an embedded CPU chip, the MX27 chip integrates H. 264 hardware codec video processing unit. From the hardware design and software design of the system, the design of video capture, compression, storage, transmission and system control of the system is introduced. Experiments show that the system has high integration, low cost, low power consumption, multiple functions and powerful, and has broad application prospects in the field of mobile video surveillance.
Keywords: embedded; i. MX27; H. 264; video codec; wireless transmission
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0 Introduction i. The Mx27 multimedia application processor is the latest addition to Freescale Semiconductor's DragonBall family, with integrated H. 264/MPEG4/H. 263 full-duplex hardware codec video processing unit, can be widely used in video surveillance, digital video recorders, network advertising machines, V2IP video phones, IPTV set-top boxes, smart phones, portable multimedia players, mobile TV, car multimedia products.
Designed based on i. The MX27's mobile video surveillance terminal is used in public transit video surveillance systems. The video data and GPS location information collected by the terminal can be transmitted to the bus dispatch monitoring center in real time. In the case of poor network, the video data and GPS location information can also be saved locally, and the high-speed transmission can be concentrated through the WIFI wireless network after the bus arrives at the station. Go to the monitoring center.
1 Bus video monitoring system composition and function description
1.1 System Components The structure of the system is shown in Figure 1.
1.2 System function description (1) Video monitoring function. The vehicle equipment supports up to 4 cameras, which can monitor the front and rear doors and compartments before and after;
(2) GPS positioning function. The video surveillance device should obtain the current time, latitude and longitude information from the GPS device, and embed the recorded video file or video stream in the form of a time tag (ie, subtitle mode); the GPS information (1 per second) is simultaneously written to the log file, Value-added processing in the later stage: the video file saved inside the video device has a one-to-one correspondence with the GPS log file;
(3) Batch communication function. When the vehicle is located in a parking lot, station, etc. with a high-speed wireless network such as WIFI/WinMax, it can enter the background data transmission working mode at any time. The transmitted content includes video files and GPS logs;
(4) Real-time communication function. When the terminal is equipped with the GPRS/CDMA network communication module function, real-time video data and GPS location information can be transmitted.
2 Mobile video surveillance terminal hardware design Mobile video surveillance transmission terminal adopts i. The MX27 is the core device, and the GPS module and WIFI module are expanded to realize the functions of collecting, storing and wirelessly transmitting mobile video. At the same time, the real-time location of the mobile device can be accurately located through the GPS information.
The system hardware structure is shown in Figure 2.
3 Mobile video surveillance terminal software design The terminal system uses embedded Linux operating system to improve service reliability and system efficiency. The main flow chart of the software is shown in Figure 3.
3.1 terminal application software
3.1.1 Video acquisition, encoding, storage Video coding using H. The 264 standard improves higher video clarity with less data. Video local storage uses a large-capacity SD card or USB flash drive. Do not use a mobile hard disk to avoid damage to the mobile hard disk caused by vibration during bus operation.
3.1.2 Wireless network transmission The terminal system is designed with WIFI high-speed wireless network and GPRS/CDMA network to adapt to different applications. WIFI wireless network is used for high-speed data transmission in places where WIFI hotspots are everywhere. In other cases, data can be transmitted through GPRS/CDMA wireless network.
3.1.3 Acquisition and processing of GPS information and other information The terminal system saves real-time GPS information every second and synchronizes time with video data. At the same time, other peripheral signals such as alarm detection are collected regularly for system processing.
3.2 Key Technology Implementation Principles
3.2.1 Video real-time transmission processing mechanism In the case of unstable or poor network bandwidth, in order to ensure the integrity and real-time performance of the video data transmitted by the network video server to the server as much as possible, the system adopts a dual processing mechanism:
(1) Compare the number of data packets in the video history buffer per unit time. If the number of data packets is found to be greater than 500 packets, perform a clear history buffer operation, and then close the open encoder to encode a new IDR frame for use. transmission;
(2) Timing comparison between the time of the current coded frame and the time of the data packet to be sent. If the time is greater than 5 s, the operation of clearing the history buffer is performed, and the encoder is turned off again to encode a new IDR frame. For transmission;
(3) In addition, in order to ensure the full use of the bandwidth, the code stream transmitted to the server can be played normally. Now, the integrity judgment of the I frame is added when the history buffer is cleared, and the currently transmitted video data is not the I frame. Perform the operation of clearing the history buffer;
3.2.2 Specific implementation of the video capture and encoding part
4 Conclusion This article describes the basis based on i. The implementation principle of MX27 mobile video surveillance terminal and its application in bus dispatch monitoring mainly introduces the design scheme and implementation method of mobile video surveillance terminal, and describes the implementation of some key technologies in detail. The system has been tested in bus monitoring and has achieved good results.
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