The D600 Firmware Upgrade Removes HDMI Output LimitsWhen the D600 launched it was advertised as being capable of impressive video recording, but those who purchased it for that purpose were met with a bit of a surprise. As it turns out, while the camera could record in 1080p, the resulting video was scaled to fit 95 percent of the screen, leaving black bars on the top, bottom, and sides. It's a very strange choice from Nikon, but thanks to a new firmware update, it's not something you'll have to worry about anymore.
According to Nikon's patch notes, "Frame output size has been changed from 95% to 100% when movie live view display is changed to "Information off" and an HDMI-compatible device is connected." The new firmware also brings some minor improvements and bug fixes, but nothing else as noteworthy as this.
You can download update 1.01 directly from Nikon.