Numerous articles have discussed the respective advantages and disadvantages of network cameras and SDI cameras. Both will find applications in their respective fields for a long time to come, and neither can simply replace the other. As for the foreseeable future, no one can guarantee that certain technical barriers will not be broken through, just as what happened to optical‑fiber transmission technology. Multiple types of equipment may exist for the same video application, owing to the need to adapt to local conditions in different environments. Compared with IP cameras, SDI cameras feature better technical stability and simpler circuits, hence higher product reliability. Below, the editor of Kaimorui explains the construction and implementation principle of SDI cameras.

The construction and implementation principle of SDI cameras are as follows:

1. Scrambled Non‑Return‑to‑Zero Inverted (NRZI) code is adopted to replace early block coding, complying with SMPTE‑259M and EBU‑Tech‑3267 standards. These standards cover digital composite and digital component signals including digital audio.
2. Before transmission, the original data stream is scrambled and converted into NRZI code to ensure reliable recovery of raw data at the receiving end. Conceptually, the digital serial interface can be regarded as a base‑band signal modulation scheme.
3. The SDI interface supports serial digital component signals at 270 Mb/s, and can transmit 360 Mb/s signals for 16:9‑format images. NRZI code is a polarity‑sensitive code, where "1" and "0" represent high and low electrical levels respectively. Long sequences of consecutive "1"s or "0"s will interfere with clock extraction from digital signals at the receiving end. Since the serial digital signal interface does not transmit clock signals separately, the receiving end must extract clock signals from the digital data stream. Therefore, NRZI code is used, in which "1" and "0" indicate the presence or absence of level transitions.
4. When receiving the NRZI code stream, data can be restored by detecting level transitions. Even an all‑"1" signal only produces a signal frequency half of the original clock frequency. Scrambling further reduces the chance of consecutive "1"s and cuts down high‑frequency components. At the receiving end of the data stream, an SDI decoder recovers the original data stream from the NRZI code stream.
5. The SDI interface cannot directly transmit compressed digital signals. Compressed signals played back from digital video recorders, hard disks and other devices must be decompressed before output via the SDI interface to access the SDI system. Repeated decompression and compression will degrade image quality and increase latency. For this reason, digital video recorders and non‑linear editing systems of various formats have defined their own interfaces dedicated to direct transmission of compressed digital signals.

This wraps up the introduction to the construction and implementation principle from http://www.cmr‑cctv.com/. We hope the above content is helpful. To learn more about SDI cameras, please visit the News Center on the official Kaimorui website.