Technique of the Netcam (Part 2)
Part 1

To compensate the mentioned disadvantages of low upstream data rates, the network camera has buffers that can store DVD quality images for a defined time so that the intruder in the monitored room can be filmed in a high quality. The images are then sent out of the danger area via the network. The responsiveness of the camera for starting the image storage, the minimum size of the moving object to be perceived as well as the image advance time can be adjusted individually. An alternative solution is to use dedicated video servers that can record up to 100 frames per second over a long period of time which can be accessed remotely later.

Network cameras also need sufficient light. A good shot requires at least 200 lux. 1 lux corresponds to the brightness of a candle. Normal office light has 500 lux. Aperture and exposure time can be adjusted to the existing lighting conditions. The aperture is usually tracked automatically. The shutter speed is fixed at 1/60 second. Only in the system other times can be set. Non-visually detectable IR lamps are used in the dark. At the same time, the camera is switched to black and white shots.

Image compression is done in MPEG-4 or Motion JPEG format. MPEG-4 only transmits parts of a recording that differ from previous recordings, e.g. a person moves in front of a stationary background. The licensed image technology MPEG-4 thus requires a lower bandwidth. On the other hand, Motion JPEG compresses the entire image and guarantees a higher image quality with a larger amount of data.

The quality of the broadband router between the IP camera and the Internet determines the reliability of the camera. Although simple broadband routers allow a functioning Internet access for a PC, they do not always meet the requirements for operating the network cameras.

The network provider changes the IP addresses with each new visitor. If a computer accesses the Internet, this is not a problem; one is identified to the network provider with its access data. But the camera is not found from outside of the Internet; if not a static (fixed) IP address has been agreed with the network provider. Static IP addresses are usually charged. Remedy provides the installation of a DynDNS client software. It is an Internet service that allows you to set a fixed hostname as a pseudonym for a changing IP address. This service assumes the task of always addressing the network camera with the same hostname, for example, Camera5. Server1.com.

The images of a network camera can be set with a JavaScript on a website. For public areas a private continuous video recording is not allowed.

However, the advantages of the Internet also involve dangers for the network camera at the same time. Hackers try massive, hostile attacks on network cameras over the Internet. The IP address of the camera should not be visible in the source code. Only an encrypted access provides some protection.