How to deinterlace video on a Mac
If moving objects in your footage have horizontal comb teeth along their edges while everything stationary looks fine, the video is interlaced. Deinterlace it before you do anything else to it — every other operation treats those teeth as detail worth preserving.
What interlacing is
Broadcast television could not transmit enough bandwidth for full frames at a smooth rate, so it sent half of each frame at a time: all the odd-numbered lines, then all the even ones, a fiftieth or sixtieth of a second later. On a CRT this worked, because the phosphors and your eye blended the two fields into one apparently complete image.
Modern displays do not work that way. They show whole frames, so the two fields — captured at genuinely different moments — get displayed simultaneously. Anything that moved between them appears twice, offset, interleaved a line at a time. That is the comb.
It is invisible on static shots, which is the trap. A talking-head interview can look completely fine until someone waves, and then a third of the frame turns into a zipper.
Where it comes from
| Source | Interlaced? |
|---|---|
| VHS, Hi8, MiniDV camcorder tape | Almost always |
| DVD (especially TV recordings) | Usually |
| Broadcast capture, 1080i | Yes — the "i" says so |
| Old digital camcorders, 60i mode | Yes |
| Anything shot on a phone | No |
| Modern cameras, 1080p / 4K | No |
The two ways to fix it, and what each costs
Blend or discard. Throw away one field and interpolate the missing lines back. You keep the original frame rate and lose real vertical resolution — a 1080i source becomes something closer to 540 lines of genuine detail, resampled back up. Simple, fast, slightly soft.
Bob, or field doubling. Treat each field as its own frame, so 50 fields per second become 50 frames per second. You keep the full temporal smoothness — motion looks genuinely fluid, which is what interlacing was buying in the first place — at the cost of doubling the frame rate, which changes how the footage cuts against anything else.
For home video and archive restoration, the first is usually right: it preserves the frame rate the rest of your edit expects. For sport or anything where the motion itself is the content, the second preserves something real that the first discards.
There is no third option that loses nothing. The information genuinely was captured at two different instants, and any single frame you produce is a compromise between them.
Why it has to come first
An AI upscaler has no concept of fields. Hand it a combed frame and it sees a regular high-contrast horizontal pattern — exactly what it has been trained to preserve and enhance — and it will render those teeth sharper and more permanent than they were. Denoisers make the same mistake in reverse, reading the regular pattern as structure and protecting it.
Once either has run, the combing is no longer a separable artefact. It is part of the picture.
The check that takes ten seconds
- Scrub to a shot with real movement — a person walking, a car, a pan.
- Pause and zoom in on a moving edge.
- Teeth on the moving edge and clean stationary background means interlaced. Uniform softness everywhere with no teeth means it is progressive and merely soft, which is a different problem with a different fix.
Crisp does not deinterlace. If your tape capture is interlaced, deinterlace it first with the tool in step 1 — then bring the progressive file here for the denoise and the upscale on export.