1.The amount of storage required for holding the video depends on the number of cameras, the resolution (image size), the frames/sec, the type of compression used, the percentage of time there is motion, and the length of time you want to store the video. Here’s how you estimate the storage –
Number of Cameras: The video from many different cameras can be stored on one hard drive and then retrieved according to the identity of the camera and the time marker. Obviously 4 cameras will require twice as much storage as 2 cameras.
The Resolution: Resolution determines how much information you will store for each frame of video. The higher the resolution the more storage it takes up. You should first determine the resolution you will need. Lower resolution if you only need to see that a person walked by. For example the Apexis camera APM-J011-WS is capable of 640 x 480 resolutions. This is high enough to allow a user to pan/tilt even after the video has been stored.
Frame rate: The number of frames per second relates to how smooth the video appears. Video viewed at 30 frames per second looks like your TV, but uses up quite a lot of storage. For example, if you store 100 KB per frame and the frame rate was 30 frames per second, you would be storing a total of 3000 KB per second (using MJPEG compression). That’s 180 MB/minute or 10.8 GB/hour or over 259 GB/day. If you record at 1 frame/sec (instead of 30 frames/sec) you only use 8.64 GB/day. Make sure you understand what you are viewing before deciding the frame rate. If you are viewing people walking around, then 5 fps or less is adequate; if you are viewing fast moving vehicles, then maybe 20fps or more is required.
Motion Detection: The Storage requirement can be reduced by using motion detection. Motion detection can be enabled by the camera or by software (like NetDVR) running on your computer. In this case the video is recorded only when motion is detected. For example if motion is not detected 25% of the time, the storage requirement is reduced by 25%.
Length of time: The video can be stored for a period of time and then over written. For example if you stored video for two days, at the end of the second day new video would start replacing the video that was 48 hours old. The more time stored, the more storage required.
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