The JVC ProHD-4601 HDMI to SDI Converter converts an HDMI input to two SDI outputs uncompressed, with audio embedded and in either HD or SD, whichever the original signal is in. With two SDI outputs available, you can send one HDMI signal to two SDI devices at the same time. For example, you can stream a camera signal, from the camera's HDMI output, simultaneously to an SDI recorder and to an SDI monitor.
An important benefit of SDI is long transmission distances. SDI can carry HD for 75 ft and SD for 300 ft. If you're shooting a scene in one room, you can monitor it in another.