I. INTRODUCTION With the development of science and technology, vehicles have become an indispensable part of people's lives, and they have appeared in various places as a manned tool. The rapid growth in demand for various types of vehicle safety has led to the rapid growth of the automotive monitoring industry. We often hear reports that the flight attendants are not paying tickets or giving fake tickets, that there are more cases of looting on the vehicles, and disputes over traffic accidents. These cases are difficult to solve due to difficulties in obtaining evidence on the spot. If you can record the situation inside and outside the car at any time, as a memory, assessment certificate, evidence and other purposes, it will be able to solve the above problems. Digital car DVRs have received wide attention as a new high-tech product in the surveillance industry. It is an embedded digital hard disk recorder that integrates digital video recording, monitoring, entertainment, advertising and other functions on mobile vehicles such as trains and automobiles. At present, digital hard disk recorders that generally provide hard disk or CF card as a single storage device in China are mostly MPEG2 hard compression coding, which has the disadvantages of high code stream, large capacity hard disk and unsuitable transmission. Most DVRs use ordinary hard disk or notebook hard disk as storage medium. Due to the mechanical characteristics of the hard disk, there are problems such as unstable video recording and easy damage of the hard disk, which seriously affects the reliability and stability of the car video recorder. There are also a small number of single CF cards used as storage media, and there is a disadvantage that the capacity is small and long-term video data cannot be saved. This article refers to the address: http:// In order to achieve the above functions, this design uses two high-performance DSPs as the core components to form the system. One DSP is a slave device, which mainly implements four channels of up to 1/2D1 MPGE4 encoding; one DSP is the main device, which mainly completes network transmission. Applications such as encoding, playback, playback of commercials, storage, control, output, and network transmission. The specific implementation is shown in the following figure: Among them, the DSP uses the NexperiaTM series of high-definition media processor PNX1700 from Philips Electronics. It integrates media processing, network connectivity and display enhancements on a single chip and is designed to deliver unprecedented quality for streaming movies, news, digital photos and TV shows. The PNX1700 delivers twice the performance of the PNX1500 while ensuring software and hardware compatibility. Digitally connected home devices with the PNX1700 include IP set-top boxes, digital media adapters, personal video recorders, video phones and televisions. Since the master/slave DSP has two video inputs, a total of four video inputs can be realized, but the image data exchange needs to be performed through PCI, so that the on-site display of four images and the rational allocation of resources can be realized. That is, after the main DSP captures the video data, it must write to the memory of the slave DSP through DMA, and inform the slave DSP through the interrupt; and after the video data is collected from the DSP, the master DSP must also be notified by the interrupt to read the data. In this way, 4-picture live display and 4-way dual-stream MPEG4 encoding design can be realized, and the burden on the main DSP can be reduced, so that the main DSP can have more resources to implement value-added applications, such as advertising video playback, GPS driving positioning. And web applications, etc. Figure 4 is a schematic diagram of the video stream processing flow of the main DSP program. As can be seen from Figure 4, after receiving the video capture completion interrupt, the main program not only needs to display the scene, but also writes the memory from the DSP through the PCI DMA and sends it. The interrupt notification is from the DSP; if it is necessary to display the image data acquired from the DSP, it is also necessary to process the interrupt request from the DSP, and the DMA of the PCI can be used to read the image data buffered from the DSP memory, thereby realizing any single or multi-picture synthesis. The scene shows. If dual stream transmission is required, then coded transmission is possible. Figure 5 is a schematic diagram of the main DSP program recording data storage and playback process. For off-board applications, the recorded data can be directly stored on a large-capacity hard disk after being processed by the file system. However, due to the strong vibration in the vehicle environment, not only is the reading and writing unreliable, but also the mechanical hard disk is easily damaged. Therefore, this program has designed a unique automatic parking backup function, that is, the recording data generated during the driving process is temporarily passed through the dedicated file system. Saved in the CF card, when the system detects the parking state, then wake up the hard disk and transfer the CF card recording data to the hard disk, so that the hard disk does not need complicated and expensive suspension system, no matter how bad the road conditions will not damage The hard disk can easily and reliably realize the long-term preservation of the driving video data, and can greatly improve the reliability and stability of the video recorder and prolong the service life of the hard disk. Video data can be backed up via a network and a USB disk, and can be burned with a recorder for long-term storage. Nanning Goodman Technology Co.,Ltd , https://www.goodmentech.com
This paper proposes a new design scheme for a car digital hard disk recorder, which can solve the above problems well. Not only can high-definition recording of the scene environment on the car (up to DVD quality), but also low-stream streaming at the same time; CF card is used as storage device during driving, and automatic parking backup strategy is adopted to avoid the driving process. The use of mechanical hard drives greatly improves the reliability and stability of the in-vehicle digital hard disk recorder. The digital hard disk recorder also has strong expansion capabilities such as advertising video playing and driving records, and has broad application prospects and value-added application space, and can be fully expanded into a vehicle platform of two sets of monitoring, driving records, navigation and multimedia applications. Replace the existing car player.
Second, the overall design of the system This program is mainly for vehicle application design, mainly to achieve the following functions:
1. Realize four-way real-time audio and video synchronization MPEG4 high-definition video, which can realize duplex playback and simultaneous two-way playback.
2, to achieve a variety of recording modes, such as manual recording, timing recording, alarm recording, driving status (such as brakes, overspeed and reversing, etc.) recording, detection of video and pre-recording for more than 30 seconds.
3. Realize four-way low-rate remote transmission, and realize remote wireless transmission through WI-FI or GPRS for remote monitoring.
4. Implement high-speed USB2.0 interface, provide recording, playback and fast backup of USB disk devices.
5. Support both CF card and IDE hard disk to realize reliable automatic parking backup function, which improves reliability and stability.
6. Realize remote uploading of alarm events and driving status, realize network functions such as remote monitoring and remote backup, and provide wireless network support.
7, to achieve dual-head display output, that is, support two independent video output at the same time, such as one way can be used to play advertising movies, all the way can be used to watch the scene and playback.
The following figure shows the functional block diagram of a four-way digital hard disk recorder: 
Based on the powerful processing capabilities of the PNX1700, a PNX1700 can theoretically perform 8-channel CIF MPEG4 encoding. In addition, it provides a number of video-specific functions, such as video filtering, De-interlace processing, and high-resolution display output, to meet the needs of the application. The OSD function, etc., provides a network and IDE interface, and also provides two video input/output interfaces. The PNX1700 also has a PCI/XIO bus that provides excellent expansion capabilities such as USB, WI-FI, and more.
Third, the software design This program uses the pSOS embedded operating system provided by the Nexperia platform. Since this operating system is a dedicated operating system provided by philips, it has mature large-scale applications and has good performance on the PNX1700, such as real-time and stable. Sex and scalability are not worse than other commercial embedded operating systems. The program is divided into two parts, one is from the program, relatively simple, mainly the realization of 4-way coding; the other part is the design of the main program, which is more complicated, mainly realizes transmission coding, file storage management, playback and control.
Figure 3 is a schematic diagram of the software processing flow from the program. As can be seen from Figure 3, the main work of the program is to encode the video and audio data. Two of the image data is provided by the main DSP and notified by the PCI interrupt. Since the PNX1700 supports 4-channel stereo acquisition, audio data can be acquired locally. When the encoding is completed, the data performs the necessary buffer processing and sends an interrupt to notify the main DSP. After receiving the interrupt request, the main DSP actively reads and processes the file system to complete the storage. 
If a remote network monitoring center is provided, it can be remotely monitored through a wireless network such as GPRS to build a complete mobile device monitoring network system.
Fourth, value-added applications For the automotive application market, the value-added applications of digital video recorders have a huge application space, such as advertising, video, GPS navigation, GPRS remote transmission and driving records (car black box). Due to the dual DSP design, the system has rich interface resources and DSP resources, which provides sufficient resource space for value-added applications. In particular, the dual output design allows playback of the commercial video and preview/playback video data without affecting each other.
V. Summary Car-mounted DVRs as monitoring devices suitable for vehicles. With the increase of social recognition and the continuous improvement of its functions, its scope of application will become wider and wider, and its role will become larger and larger. It will be widely used not only in long-distance buses and buses, but also in pick-up and drop-off trains for trains, ships, ambulances, fire engines, public security traffic police vehicles, material transport vehicles, station wagons, institutions, schools, kindergartens, etc. Has a very wide range of uses. The car digital video recorder will play a very important role in making the society more civilized and safer.
The author of this article is innovative:
1) Based on two high-performance DSPs, the advanced MPEG4 compression algorithm is used to form a four-channel real-time dual-stream multi-function digital digital hard disk recorder through PCI.
2) When using CF card as the storage device, use the automatic parking backup strategy to avoid the use of mechanical hard disk during the driving process, which greatly improves the reliability of the digital DVR.