Drop Frame vs. Non-Drop Frame Caption
Not all 29.97 fps video is drop frame. Some video is non-drop frame (NDF), which means that the timecode does not account for the difference in video time vs. real time. If you are captioning your video, it is important to know whether your video file is drop frame or non-drop frame so that your captions are accurately synched with the timing of the media. At the end of a real-time hour, a DF video will have run 01:00, while at the end of a real-time hour, a NDF video will have run 00:59:56:12. If you caption a DF video with NDF captions, the captions will not be synched with the video and will get more and more out of sync as time goes on.
NDF files are written with all colons (hh:mm:ss:ff) while DF files are written with either a semi-colon or a period between the seconds and frames (hh:mm:ss;ff or hh:mm:ss.ff).