What is an SDI connector, and why would I use one?
SDI connectors are professional high-definition video ports.
One of the great strengths of the SDI format is that it enables you to send HD video and audio signals through 300 feet of cable (HDMI is limited to 30 feet).
An example of when you would need this is when the camera is shooting in one area, and an additional video monitor is set up and fed the signal from the camera a great distance away (producers and other crew members often need to view a shoot remotely, without interfering on set).
Unlike HDMI, SDI connectors lock into place to avoid accidental disconnections.