What is frame-accurate editing?
Frame-accurate editing means every cut lands on one exact whole frame, and that frame stays the same whether you play the cut or export it. It is also the frame someone else gets when you hand the edit on. It matters because a single frame can be the difference between a clean cut and a visible flash, or between a word and a clipped syllable. A frame-accurate editor also keeps timecode exact, so a note at a given time points to the same picture for everyone.
Video is a sequence of still pictures, usually 24 or 25 of them each second. Much North American television runs at 30, or in practice the slightly slower 29.97. An edit is a decision about which of those pictures comes next. Frame accuracy simply means the software honours that decision exactly.
Why a single frame matters
At 24 frames a second, one frame lasts about 42 thousandths of a second. That sounds like nothing, but people notice it.
- Flash frames. Leave one stray frame of the wrong shot at a cut and viewers see a flicker.
- Dialogue. Cutting a frame early can clip the start of a word. Cutting late can leave a breath or a lip movement.
- Action. Match cuts on movement only feel smooth when they meet on the right frame.
- Hand-offs. When sound and colour rebuild your cut from an AAF or EDL, they need the same frames you chose. A cut that is one frame out in their system means their work will not line up with yours.
Timecode and drop-frame
Timecode labels each frame as hours, minutes, seconds and frames, so that everyone can refer to the same picture.
At 29.97 frames a second, there are slightly fewer frames in an hour than the labels assume. Drop-frame timecode corrects for this by skipping two frame numbers at the start of each minute, except every tenth minute. No pictures are thrown away. Only the labels skip. Over a long day of footage, getting this wrong by even a little means notes and hand-offs point to the wrong picture.
How to tell if an editor is frame accurate
- Step through a cut one frame at a time. The outgoing and incoming frames should be exactly what you expect, with nothing in between.
- Export and check. Step through the same cut in the exported file. It should match.
- Check timecode late in a long clip. Compare the editor’s timecode against the camera’s at the end of a long recording, especially at 29.97 drop-frame.
- Watch sync over time. On a long take, check that lips still match the sound at the end as well as the start.
How B/side handles it
In B/side, every position is a whole frame. You cannot place a cut between frames, so what you see when you step to a cut is the cut. Drop-frame timecode stays exact across a full day, and sound stays in sync with picture.
Trim mode handles ripple and roll trims, including asymmetrical ones. A live two-up shows the outgoing and incoming frames, and every nudge previews before it is applied. Notes from clients and producers are written on the frame they were watching, so everyone is pointing at the same picture.
When it matters less
For a quick social clip with music under it, a frame here or there rarely shows. Frame accuracy becomes essential once you cut dialogue, and certainly once you hand the edit to someone else.
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