Drop-frame timecode
Drop-frame timecode (DF)
A timecode convention for 29.97 fps video that drops 2 frame numbers per minute (except every 10th) to keep timecode aligned with real time.
In depth
Drop-frame timecode is a numbering trick for 29.97 fps NTSC video. Real time runs at 30 fps; NTSC runs at 29.97 fps. If you counted every frame as a frame number, after an hour your displayed timecode would be 3.6 seconds ahead of the wall clock. Drop-frame skips two frame numbers at the start of every minute except every tenth minute, keeping displayed timecode within ±2 frames of real time over a one-hour broadcast. Subtitle SRTs use real time, not drop-frame numbering, so the only place this matters is when round-tripping captions through a broadcast NLE.
When to use it
Care about drop-frame when working with broadcast deliverables, EDLs, or AAFs from a broadcast NLE. For social and streaming workflows, ignore it — SRT real-time always wins.
Frequently asked
Is drop-frame the same as variable frame rate?+
No. Drop-frame is a numbering scheme on top of constant 29.97 fps. Variable frame rate (VFR) is a recording where the actual fps changes scene to scene, common in iPhone footage.
Will drop-frame affect my SRT timing?+
Only if your editor exports SRTs based on timecode rather than runtime. SoCaptions and most modern tools export based on actual elapsed time, sidestepping the issue.