Ahmed Shakib - Technician - 2M CCTV
HD-SDI or High Definition Serial Digital Interface is a newer kind of video interface run by SMPTE (Society of Motion Picture and Television Engineers) and an upgrade to the current SD-SDI (Standard Definition Serial Digital Interface). An HD-SDI camera allows you the ability to have megapixel in a standalone DVR. HD-SDI also gives you the ability to upgrade your system without rerunning coax cables. Compare to upgrading your system to IP cameras, which utilize more bandwidth and higher storage, HD-SDI uses 575kbyte and half the upload broadband speed. This makes for an easy transition to higher-end megapixel systems, with half of the cost of a hybrid DVR system.
IP cameras nowadays are becoming more synonymous with higher end HD or High Definition video resolutions (Further Reading: CCTV Resolution for Analog, IP, and DVRs). You might have heard of phrases like “megapixel” that are associated with IP cameras. Although not all IP cameras are megapixel, the term is used accurately enough, because the video signal from the IP camera is transmitted through the network in digital form, which means the NVR (Network Video Recorder) will not need to decode the video footage back to digital.
The standard coax cable can only carry a signal with up to 270-325 megabits of data, resolution up to 480p, and it uses the old TV lines protocol to describe its resolution. Your DVR (digital video recorder) will only provide you with standard definition video out to your monitor. If you want to achieve higher video definition, you will need to upgrade your DVR to an NVR or Hybrid system that can handle IP cameras. If you prefer a standalone system and a computer-based DVR is not your style, there is a fairly new technology, called “HD-SDI” that can handle higher resolution or megapixel cameras. This device is in its infancy and uses pure digital signal to transfer the video signal to the video recorder.
HD-SDI: Origins and Usage
Since 1990, the Motion Picture and Television industries have used high definition serial digital interface because, due to their need of recording higher resolution videos, it gave them the ability to move uncompressed and unfiltered recorded videos from their video camera to the video processor. This video interface can transmit data up to 2.97gbit. HD-SDI is mainly used for higher output video transitioning and can output video resolution up to 1080i. Originally, HD-SDI had limited work scope; this meant the digital video signal could only be transmitted, in an uncompressed and unencrypted form, within the production facility.
Comparison using the Veilux VB-11IRC68L2810D-HD High Resolution Infrared Camera
HD-SDI, just like SD Serial Digital Interface, uses coax cable with impeded BNC connection with standard nominal impedance of 75 ohms. For surveillance systems, this means you could use RG-59 or coax and a BNC connector to run your cable. The main difference with HD-SDI vs. the standard analog is that HD-SDI cameras will have to be connected to a DVR with an HD-SDI video input. Due to the higher video transmission, a DVR with the ability to read HD-SDI video signal will require dedicated channels that cannot be used with your average analog camera. HD-SDI can transmit video signals of at least 100 m with RG-59 cable before requiring repeaters to boost its signal.
Improved Video Quality
HD-SDI video signal has a few advantages over IP and analog cameras. For an analog camera, as you might have guessed, HD-SDI has improved video quality. Normally, analog cameras transmit their video footage in an electric signal which is then decoded to digital data in the video recorder. This essentially means that the video footage will lose some quality as it is processed and displayed on your LCD monitor. It further loses quality as the digital video recorder compresses and saves the video as MPEG4 on your hard drive (Further Reading: Learn about MPEG4 and H.264 video compression for DVRs).
Facilitated Video Transmission
Unlike analog cameras, HD-SDI does not lose video footage quality as the electrical signal is transmitted through the BNC cable, as it uses Non-Return to Zero Inverted (or NRZI) to encode the video signal. NRZI helps facilitate the transmission of the encoded video back to its original data form. In a way, HD-SDI and IP cameras are both very similar in the way that they both transmit video digitally. Unlike IP cameras however, HD-SDI has better zero recovery and lower latency when zooming in digitally, as the video is processed digitally at the DVR.