On May 10, 2021, the mother of a microblogging user @forty-nine middle school students (formerly known as @lifeislikeabubble) said that her son, who was studying in Chengdu forty-nine middle school, died accidentally at school, and when looking at the monitoring, “the only thing that happened was that there was no monitoring”.
In the early morning of May 11, @Chengdu Education released a briefing, saying that through the site survey, access to monitoring and other methods, after a thorough investigation, the student was found to have fallen to his death from a height is a personal behavior.
But parents initially did not agree with this statement and demanded to see the full video. The CCTV network and CCTV news also published comments, questioning “why the key video surveillance is missing”. The loss of the surveillance video as key evidence once became one of the most confusing details.
Tonight at 19:43, @peacefulchenghua released a briefing, said through the investigation of monitoring, electronic data survey and other means, determined that Lin Moumou fell dead, excluding criminal cases.
The incident for the controversy of the loss of monitoring is considered to be over, as the key evidence to restore the incident, the proper retention of surveillance video is extremely important. But the event of lost surveillance video has happened in many news.
Surveillance video is actually not so easy to lose, accidental loss often has a mature data recovery methods.
Video is overwritten
In various cases of surveillance video loss, “video was overwritten” is probably the most commonly heard reason. Due to the limited capacity of the storage device of the surveillance system, when the video files are stored near the capacity limit, the new video files will indeed overwrite the earlier files. Moreover, the new files are stored directly in the place of the old files, and the old files are directly erased, making it almost impossible to recover the old files once this happens.
However, different application scenarios have corresponding “minimum storage length” regulations. If the surveillance system can only store 2 minutes of video, then the system is not meaningful. For example, the current car recorder, generally equipped with storage space can guarantee to accommodate 24 hours of video recording; after all, for car owners to come, before and after the accident is the focus of the complete video, very early safety driving video is usually not very meaningful.
The car recorder will automatically overwrite earlier videos.
In September 2020, the Chengdu Public Construction Office, in conjunction with the city’s Education Bureau and other units, issued the “Technical Guidelines for the Construction of Ordinary Primary and Secondary Schools in Chengdu”, which clearly states that “monitoring data storage is not less than 90 days” on campus, which also ensures the possibility of backtracking monitoring videos.
Video was deleted by mistake
In order to ensure reliability, the monitoring system does not use ordinary computer hard disk storage data, but will choose a more professional disk array – it can directly detect the integrity of the data, and even directly provide backup to ensure stable and reliable data storage. And the traditional file is different, monitoring video is not an isolated large file, but a continuous stream of data. One can retrieve data from different zones through the software, and when a failure is encountered, only a small amount of data is affected, without affecting other data.
Surveillance systems are generally equipped with special operating software for adjusting cameras, manipulating surveillance files, etc. In order to avoid accidental deletion, there will be a secondary confirmation window when deleting files in the operating software. Therefore, the possibility of “accidentally emptying the recycle bin after pressing the Delete key” is not very likely.
Moreover, the professional monitoring system is also equipped with data recovery functions. Even if you use an ordinary computer mechanical hard drive to store files, you can recover mistakenly deleted files in a short time. When we delete a file, we just tell the system that “the place occupied by this file is free for use”, but the original data remains here until new data occupies this place. So in the short term, there is still a good chance to get back the deleted data.
Sometimes, surveillance is lost not because the files are gone, but because the files are still there, but nothing is recorded. This situation is usually the camera, transmission cable is damaged. At this time, the host or remote server collection side is still collecting data, but nothing can be collected, only a full screen of black.
In September 2020, Zhejiang Ninghai, a girl fell to her death in the school, the monitoring of its fall location due to failure of the black screen.
For security level monitoring equipment, once this happens, it is quite dangerous. By automatically detecting the difference between the front and back frame images, while calculating the color distribution of the video image, the monitoring device itself can know if there is a black screen situation, so it can issue an alarm with a prompt.
In the movie, the protagonist just step in advance, a pull of the electric switch, the monitoring can be all wasted …… real-life power outages?
In order to prevent sudden power outages on the data being stored, monitoring systems are equipped with UPS power supply, which is the power supply after a power outage, can continue to supply power through the power storage device after a power outage. Operators are able to properly handle the system and save the data before shutting down normally. In schools, the video surveillance system needs to be guaranteed to work properly for one hour after a power outage.
Power outages do affect the work of the surveillance system, but as a key security equipment, engineers have also set up a corresponding plan for the surveillance system, will be the first time to remind the staff responsible for monitoring system problems.
In order to avoid “monitoring happens to be broken” situation, not only monitoring equipment self-checking, data storage capabilities continue to upgrade, monitoring systems also began to network, the video recordings in the cloud server backup. New technology allows the storage of surveillance video is guaranteed, so that the loss is not easy.
The development of technology is to allow us to encounter an accident with more protection, after all, when the accident comes, we need not a pendulum machine, but a record that can restore the scene and reveal the truth.