As one of the most important functions of vehicle-mounted video surveillance equipment, audio and video coding and decoding capability is one of the key capabilities to consider vehicle-mounted digital video recorder. In this regard, there is no difference in essence between vehicular video recorders and ordinary video recorders. Mainstream video codec chips are chosen and mainstream codec formats are adopted to seek the greatest harmony between coding compression efficiency and image sharpness. At present, most decoding methods of VCR are based on H. 264 standard.
In the use and acquisition of video, there is a big difference between ordinary DVR and vehicle DVR. Ordinary DVR is often used in fixed places, fixed devices, not easy to move, can be displayed locally, or through the fixed network (ADSL) access to the monitoring network, any observation point in the network can access the DVR host through the network. Vehicle DVR can only access the monitoring network through 3G/4G. Therefore, vehicular DVR is more concerned with the control of bit stream, while ordinary DVR is more concerned with the priority of picture quality. H.264 has high compression ratio and high quality and fluent images. Therefore, the video data compressed by H.264 needs less bandwidth and is more economical in the process of network transmission.
In order to meet the real-time online transmission of video pictures, most of the on-board devices use 3G network. Compared with 2G, which is commonly used in vehicle driving recorder, 3G mainly improves the speed of transmitting voice and data. It can better realize wireless roaming around the world and deal with image, music, video streams and other media forms. It can support different data transmission speeds, that is to say, it can be separated in indoor, outdoor and driving environments. Do not support at least 2 Mbps, 384 Kbps and 144 Kbps transmission speed (this value changes according to the network environment). With the rise of 4G network, vehicle-mounted video recording equipment has begun to use 4G as a transmission mode. The data transmission speed is faster and the amount of data that can be supported is more huge for high-definition picture transmission.
Vehicle-mounted digital video recorders can also be combined with automotive electronic related functions. For example, CAN bus technology is widely used in vehicle driving data acquisition and upload. Vehicle-mounted digital video recorders should also have CAN bus access and analysis and processing functions. The relevant information of vehicle driving can be recorded by hard disk, and important data can be analyzed and processed. In addition to adding hard disk shock absorption and reinforcement treatment, attention should also be paid to the differences between the power supply used in such projects and that of ordinary automobiles. For example, the power supply of on-board equipment for trains is mostly DC 48V or DC 110V, while the power supply for ordinary automobiles is DC 12V or DC 24V. Vehicle-mounted DVR, as the front-end core equipment of information gathering, also bears the functions of vehicle-mounted information gathering and gathering. Access to a variety of vehicle accessories, thus providing a wide range of sources of information. The inertia sensor (Fig. 1) is an electronic device for measuring vehicle acceleration and vehicle ambient temperature. By measuring the acceleration, we can know whether the driver has bad driving habits such as sudden acceleration and sudden braking when the vehicle crashes and rollovers during driving, and analyze the cause of the accident. By measuring the temperature with built-in temperature sensor, we can know the ambient temperature of the vehicle equipment and trigger the temperature alarm.