Drop-frame, done right
Timecode labels frames as HH:MM:SS:FF. At clean rates like 24, 25 and 30 fps, the label and the real clock stay in step. At 29.97 and 59.94 fps they do not: the camera actually records 30000/1001 frames a second, so counting as if it were a flat 30 drifts ahead of the wall clock by about 3.6 seconds every hour.
Drop-frame timecode fixes the labels by skipping two frame numbers (four at
59.94) at the start of every minute, except every tenth minute. No frames are lost, only labels,
and over an hour the timecode lines up with real time. Drop-frame is written with a semicolon
before the frames, like 01:00:00;00. Non-drop keeps every label
and accepts the drift, which is fine for short clips but wrong for broadcast durations.
This converter uses the standard SMPTE drop-frame calculation, so the timecode, the frame count and the real time all agree. Edit any of the three fields and the other two update. Sister tools: Unix Timestamp Converter and Time to Decimal.