If video were really 30fps, then a program that started at time code 00:00:00:00 and ended at the time code 01:00:00:00 would be one hour long. Unfortunately, video is really 29.97fps, so the aforementioned program is really longer than one hour. (The difference is 0.1%) This can really mess up broadcasters who obviously schedule things according to clock time. So, broadcasters use drop-frame time code. This version of time code skips or "drops" a number every so often so that the time code stays in sync with clock time.(posted 9079 days ago)Dropping time code numbers is inconvenient if you are trying to do time code math -- like trying to determine the length of a clip. Unless you are a broadcaster, or delivering programming primarily for broadcast, it is usually more convenient and less confusing to use non-drop time code.