The Movie Quality setting on your Nikon D7100 can be accessed via the Movie Settings option on the Shooting menu or the Live View control strip. Remember, you display the control strip by simply pressing the i button.
For this option, you can choose from two settings, High and Normal. Your choice determines how much compression is applied to the video file, which in turn affects the bit rate, or how much data is used to represent one second of video, measured in Mbps (megabits per second). A higher bit rate means better quality and larger files. On the D7100, High delivers a bit rate of 24 Mbps; Normal, 12 Mbps.
Because bit rate affects the size of the video file, it also determines the maximum length of the video clip you can create each time you press the record button. If you select High as the Movie Quality option, the maximum movie length is 20 minutes. At the Normal setting, you can record 29 minutes and 59 seconds of video at a time.
One last tip about this setting: In the Live View display, a star in the area labeled Movie Quality indicates that the High bit rate is selected. No star means that the option is set to Normal. This same star system reflects the setting in the Frame Size/Frame Rate menu screens.