Video baluns are an accessory which enables the transmission of video by transforming an unbalanced signal into a balanced signal. Normally, this unbalanced signal is transmitted using coax cable, however by transforming the signal to a balanced form, ethernet cable can now be used to carry the signal.
Why is this important? Coax cables require special shielding to minimize noise from radio frequency. While the shielding helps to mitigate the loss, the radio frequency noise makes it difficult for coax cable to carry the signal over large distances. By using a video balun, an ethernet cable can be used to transmit video for much longer distances without experiencing the same level of signal loss and at a lower price point. Some baluns even allow you to power your network over the ethernet cable making it even easier to set up your network.