A mode of the SMPTE time code designed to allow synchronization of audio with U.S. NTSC color television material.A quirk in the NTSC color standards, as implemented in the U.S., is that the frame rate is not exactly 30 frames/second; rather, it is slightly less at 29.97 frames/second.Since the SMPTE standard doesn’t allow for a frame rate that isn’t an integral number of frames per second, this mode approximates the true rate by running at 30 frames/second, but with certain specified seconds throughout each hour having only 28 or 29 frames, so that the average stays close to the true NTSC color frame rate. This makes calculating a precise number of frames between two points in time difficult, which is a good reason not to use the 30-drop frame rate on a project that isn't required to synchronize to video.

Analog NTSC broadcasting, except for a few low-power stations, has ceased in North America, so there is no longer any motivation for new productions to use the 29.97 NTSC color frame rate.

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