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Wireless Video Interfaces
Video signals come in many different forms, and there is a wide range of products to support the various types of signal interfaces. This range of offerings can best be understood by separating them into several categories, such as analog vs. digital, consumer vs. professional wireless video, and by whether or not the signal is targeted for further editing and post production versus simply being sent to a display. Each of these criteria will determine the set of applications that can be supported by each technology and device.
Wireless analog video transmission has for the most part become obsolete, due to the inefficient use of RF spectrum that was typical for these devices. Instead most analog signals today are digitized and also compressed before wireless transmission. This includes audio signals even though these signals consume much less RF bandwidth. One application where analog video signals are still widely used today is (ironically) for delivering signals from computers to displays. Formats including VGA, RGB and DVI-A are all analog in nature, and therefore are rarely transmitted in their native form over wireless networks. Several different types of converters are available that can digitize and optionally compress these analog signals to make them easier to transport over digital wireless links.
Outputs from digital video cameras of all types, including professional, prosumer and consumer models are easily adapted for long range wireless video transport. The most prevalent professional interface is SDI (Serial Digital Interface), which comes in three main versions: SD operating at 270 Mbps, HD operating near 1.5 Gbps, and 3G operating at almost 3 Gbps. Each of these is an uncompressed digital video signal, using 10-bit resolution, 4:2:2 color sampling and a standard 75 ohm BNC interface (although several other connectors are used by various camera manufacturers). SDI can be video only, but it also supports multiple embedded audio channels and various forms of metadata, such as SMPTE time code.
Another increasingly popular camera output connector is HDMI, a 19-pin connector that supports multiple bit rates and resolutions of digital video, along with multiple channels of digital audio. The major advantage of an HDMI signal is that it can be connected directly to consumer displays, which are inexpensive and offer extremely high quality for all but the most demanding applications. Note that wireless transport of HDMI signals that originate from copyrighted sources (e.g. DVDs and Blu-ray discs) may not be possible due to the encryption system known as HDCP (High-bandwidth Digital Content Protection). The HDMI connector is relatively inexpensive and low profile, but it does suffer the drawback of not having a built-in cable retention system that locks the connector in place when being used. As a result, HDMI is most often found on consumer and prosumer cameras. Captive screws can be found on HDMI connectors and equipment in higher end Professional Audiovisual applications.
Other types of video interfaces are less prevalent for wireless applications, including S-video and DVB-ASI, and have little support in the wireless product space. S-Video, being an analog, SD signal is no longer in widespread use in most organizations. DVB-ASI (Digital Video Broadcasting Asynchronous Serial Interface) is common for systems that are transporting multiple signals over a single path, but in wireless deployments it is mainly used over fixed microwave links between facilities.
