29.97 fps Non-Drop is a slightly slower version of 30 fps Non-Drop timecode. When 29.97 fps Non-Drop is used with color video, each video frame matches up with each SMPTE frame without having to use a drop-frame coding. This makes any frame number mathematics much simpler, since no frame numbers are dropped.
Some hardware and software devices do not recognize 29.97 Non-Drop as a separate frame rate. For example, any standard SMPTE-to MTC-converter does not explicitly recognize it. You must set the convertor to expect 30 fps Non-Drop instead. In fact, many devices that read SMPTE work acceptably by reading 29.97 Non-Drop if they are set to expect 30 fps Non-Drop.
Any SMPTE reader that uses the timecode numbers to make real-time calculations (as Pro Tools does when it tries to trigger and synchronize to SMPTE) also needs to know that the frame format is 29.97 and not 30 fps. Since Pro Tools allows this choice of frame rate this does not really pose a problem. The problem exists because many users cannot readily distinguish 29.97 from 30 fps.
Even though NTSC tapes only use 29.97, some production companies will distribute video work prints striped with 29.97 fps but mark them as “30 fps NTSC,” by which they actually mean 29.97 fps Non-Drop.
By the time you get the tape, you may have no idea what’s actually on it. Feeding 29.97 Non-Drop to Pro Tools when it is set for 30 fps Non-Drop will result in timing errors of about 1.8 frames per minute, causing audio playback to trigger out of sync.