Swirly Feedback

Temporal feedback and trail effects Make swirling and evolving forms driven by your video.

This ofx was originally inspired by the legendary Quantel DPE 5000 and Fairlight CVI (Computer Video Instrument). Create evolving motion trails, video feedback loops, rainbow echoes, and psychedelic swirl effects — all in real time.

The Fairlight CVI was a favorite of early video artists — relatively inexpensive with lots of capabilities, from the same Fairlight that gave us the CMI (Computer Musical Instrument) and eventually the Fairlight audio workstation that Resolve's Fairlight page is named after. The Quantel DPE 5000, on the other hand, was expensive and polished — one of the first commercially available digital video machines. Quantel's "Howl" effect was made famous in The Jacksons' Blame It On The Boogie and Earth, Wind & Fire's Let's Groove, both from the early 80s — and is very similar to the "Retro Rainbow Trails" preset here.

Every frame, the trail from the previous frame is transformed — zoomed, rotated, translated, hue-shifted, swirled — and the source is optionally composited over. The result is a continuously evolving image that builds on itself over time.

Overview

Strobe Feedback v2 can produce a wide range of looks:

• Motion Trails - Ghostly echoes that follow movement, fading over time
• Video Feedback Loops - The classic "camera pointed at a TV" tunnel effect, using zoom and rotation
• Rainbow Trails - Hue-shifting trails that cycle through the spectrum as they evolve
• Swirl Effects - Organic, animated curl noise displacement that makes trails flow like smoke or liquid
• Strobe Stamping - Source is stamped at regular intervals, with the trail evolving continuously between stamps
• Built in Luma Keyer for Free Users - We recommend using Magic Mask (or other matte sources), but the free version of Resolve doesn't include that. The built in luminance keyer lets free Resolve users generate mattes without Magic Mask. Also - if you're going for that retro look, the vintage tech used basic luminance or chroma keyers as well.

Quick Start

Select the effect from the OFX list, and drag it onto a corrector node (color page) or onto a clip (edit page).

Important!

This ofx REQUIRES an alpha source! The easiest is to use Magic Mask or the built in luma keyer, but you can use pretty much any alpha source: an externally generated alpha, one from fusion, a qualifier or a power window.

Put the alpha source into the second input, both the green and blue tabs. If you have Magic Mask (resolve studio) make a mask of your subject, and put the alpha output (the blue tab on the magic mask node) into both tabs of the ofx. If you have the free version of resolve, you can use the built in luminance keyer, which is described later in this document.

Easiest: Use the Presets!

In the "Presets and Help" section of the ofx there are two dropdowns: "Factory Presets" and "My Presets". Try out the various factory presets to get the idea of the range of effects. Some good starting points:

• Retro Rainbow Trails - Classic hue-shifting motion trails, similar to the Quantel DPE5000 "Howl" effect, seen in old-school music videos.
• Smoky / Smoky 2 / Smoky 3 - Organic, atmospheric trail effects
• Video Feedback Old School 1 & 2 - The classic TV feedback tunnel
• Rainbow Oilslick - Nice colorful random swirly motion.

Later, when you develop your own looks, you can save your own presets: give your look a name in the "Save As" field, and click "Save". Your presets will then appear in the "My Presets" dropdown.

Manual Quick Start

1. Apply the effect to your clip — from the "Academy VFX" group in the OFX list. In the color page, drag onto a corrector node. In the edit page, drag onto a clip.
2. Set up your alpha The easiest way is to drag a second corrector in, connect the source, and generate your mask. Take the Blue output of that corrector, and connect it to both the second green and second blue inputs of the corrector with the ofx applied.
3. Hit play — this is a temporal effect, so you need to play forward to see the trail build up. Scrubbing won't show the accumulated result.
4. Adjust Feedback Amount — at 1.0 (default), trails persist forever. Lower values make trails fade over time. Try 0.95 for trails that fade after a few seconds.
5. Try Zoom — set to 1.01 or 1.02 for a subtle zoom-in on each frame. This creates the classic video feedback tunnel effect.
6. Try Rotation — add 1-2 degrees for a gentle spin. Combined with zoom, this creates spiral tunnels.
7. Try Hue Shift — add 5-10 degrees for rainbow trails that cycle through the color spectrum.

Inputs

Parameters

Quantel/CVI/Feedback Group

These controls recreate the core feedback capabilities of the Quantel DPE 5000 and Fairlight CVI — the legendary machines that defined early digital video effects. The CVI's feedback loops and the Quantel's "Howl" effect were staples of 80s music videos and broadcast graphics. Each frame, the trail from the previous frame is transformed by these parameters before the new source is stamped on top.

Feedback Amount

The most fundamental control. This determines how much of the previous frame's trail survives into the current frame:

• 1.0 — Trail persists forever. Old frames never fade.
• 0.95-0.99 — Trail fades gradually. Lower values = faster fade. This is the range used in those vintage effects.
• 0.0 — No trail at all. Only the current frame is visible. This essentially turns off the ofx, but with extra steps :)

Zoom

Scale factor applied to the trail each frame. Values very close to 1.0 produce the most usable results:

• 1.0 — No zoom. Trail stays in place.
• 1.005 - 1.02 — Gentle zoom in. Creates the classic "camera pointed at a TV" feedback tunnel.
• 0.98 - 0.995 — Gentle zoom out. Trail shrinks inward each frame.

Rotation

Degrees of rotation applied to the trail each frame. Small values create spirals when combined with zoom:

• 0 — No rotation.
• 1-5 — Gentle spin. Combined with zoom, creates elegant spiral tunnels.
• Large values — Rapid spinning. Can create kaleidoscopic effects.

Shift X / Shift Y

Shifts the trail horizontally and/or vertically each frame. This creates directional motion trails — the trail slides in a direction while evolving:

• Small values (0.001 - 0.01) — Subtle drift. Trail slides slowly.
• Larger values — Aggressive sliding. Creates echo-lineup effects where you can see multiple copies of the subject lined up across the frame.

Hue Shift

Rotates the hue of the trail by this many degrees each frame. Because it accumulates, even small values create dramatic rainbow effects:

• 0 — No color change. Trail retains original colors.
• 3-10 — Gentle rainbow cycling. Trail transitions through the spectrum over many frames.
• 30+ — Rapid color cycling. Each echo is a different color.

This is the heart of the Quantel "Howl" effect and the Fairlight CVI's signature rainbow trails — a moving subject leaves a spectrum of colored ghosts behind it.

Saturation Boost

Multiplies the trail's saturation each frame:

• 1.0 — No change.
• 0.8-0.95 — Trail desaturates over time, fading to gray.
• 1.1-1.5 — Trail becomes more vivid over time. Can create intensely saturated psychedelic effects. Use sparingly — high values can blow out quickly. Or go wild. You do you. Have fun.

Blur

Applies a Gaussian blur to the trail each frame. Because it's applied every frame, even small values accumulate quickly:

• 0 — Sharp trail. Older frames remain crisp.
• 1-3 — Gentle softening. Trail gets dreamier over time.
• 5-10 — Trail dissolves into soft color fields after a few frames.

When you have blur applied, the newer frames are crisp, and the old frames are softened.

Transform Center

The pivot point for zoom and rotation transforms. By default it's at the center of the frame (0, 0 in centered aspect coordinates).

Moving the transform center off-center creates asymmetric feedback patterns — the tunnel or spiral will orbit around this point rather than the frame center.

Strobe Interval

This determines how often the current source frame is "stamped" onto the evolving trail:

• 1 — Source is stamped every frame. The trail is always topped with the current frame. Good for simple motion blur / echo effects.
• 4-8 — Source stamps periodically. Between stamps, the trail evolves on its own (zooming, rotating, swirling) without new source material. This is where the most interesting feedback effects happen.
• 15-60 — Very infrequent stamps. The trail has long periods of pure evolution, creating abstract, heavily transformed imagery before the next source stamp resets the pattern.

Live Opacity

Controls how visible the current source frame is over the trail:

• 1.0 — Full source visible. You always see the current frame clearly, with the trail behind it.
• 0.5 — Source is semi-transparent. The trail shows through the current frame.
• 0.0 — Source is invisible. You only see the evolving trail. The source still gets stamped at strobe intervals, but between stamps, only the trail is visible.

Wrap Offsets

When enabled, the trail wraps around at the frame edges instead of getting chopped off at the edges of the frame. This creates seamless tiling patterns when using translate or zoom-out, or frame filling swirls when used with the swirling effects.

Swirl Group

Animated procedural swirling that makes trails flow like smoke, liquid, or abstract organic patterns.

Swirl Strength

The main swirl control. How hard the trail is "stirred":

• 0 — No swirl.
• 1-3 — Gentle, smoky swirl. Trail flows like incense smoke.
• 3-5 — Strong displacement. Trail becomes fluid and abstract.
• Negative values — Swirl in the opposite direction.

Swirl Frequency

Controls the spatial frequency of the swirl pattern:

• Low values (0.5-1) — Large, broad swirls. The whole frame moves in sweeping arcs.
• High values (>1) — Tight, detailed vortices. Many small swirl features across the frame.

Swirl Speed

How fast the swirl pattern evolves over time:

• 0 — Frozen pattern. The whorls and eddies don't move - even though the images are still pushed through the distortion field.
• 0.5 — Gentle evolution. The swirl pattern drifts and changes slowly.
• 2-3 — Rapid evolution. The displacement field changes quickly, creating turbulent, chaotic motion.

Swirl Detail

Number of noise octaves layered together. The higher this number the more fine detail is added to the swirls.

• 1 — Smooth, simple swirl.
• 3-4 — Turbulent, detailed swirl with fine eddies.
• 6 — Maximum detail.

Swirl Warp / Swirl Warp Speed

Kinda hard to explain - without swirl warp, the swirl's sizes are uniform. If you have the swirl frequency low, they're all large. If the frequency is high, they're all small. Warp changes that. Adding warp will make some of the swirls larger, some smaller.

And, like swirl speed, this makes the effect of warp animate. So if swirl warp speed is 0, the large areas will remain large, small will remain small. Adding some swirl warp speed makes that animate (the large and small areas move around).

To understand this this more easily and visually, turn Feedback Amount to 1, swirl speed to 0, and swirl warp speed to 0 first, then experiment with the warp controls.

• Warp 0 — Uniform swirl frequency everywhere.
• Warp 2-5 — Interesting spatial variation. Some areas swirl tightly, others broadly.
• Warp Speed — How fast this modulation pattern evolves.

Luma Expand

This kinda "bloats" the trails at their most luminant parts. Not really "swirling" but that's the group it's in. Combine this with hue offset and saturation boost to get "mixing paint like" effects.

Alpha Source Group

This is pretty important to understand, so pay attention here.

It's recommended to use a mask signal for best results. Magic Mask is super easy to use, and we recommend it.

In the color page, add a corrector, and make a Magic Mask as usual. Take it's output's Blue tab (alpha), and put it into the OFX's SECOND blue AND green tabs, and you're all set.

If you have an external mask (for instance, if you're working with a chromakey from the color page or fusion), the process is quite similar - the mask goes into both of the OFX's second input's tabs.

If you don't attach an alpha source to the second input of the ofx, it will extract an alpha from the input source's luminance, which you can tweak with the clip and softness settings in the alpha section.

If you have the free version of Resolve (no magic mask), you can use the built in luma Keyer

This works best for subjects shot over black or dark backgrounds - and it's very similar to the internal keyers of the "vintage" DVEs of the past.

The keyer controls what parts of the image contribute to the trail, based on the source's luminance.

Alpha Source Modes

• Red Channel — Uses the red channel of the Second Input (external matte) input (or Source if no matte connected). This is the default.
• Alpha Channel — Uses the alpha channel of the Second (ExternalMatte) input. Useful when your matte is embedded in the alpha.
• Luminance Key — Generates a matte from the source image's luminance (Rec.709 weighted). Use the Clip and Softness controls to dial in which luminance ranges are included. It's probably best to start with the Clip Low and Softness Low to be most like a standard luminance keyer.

Clip Low / Clip High

These clip the luminance range from each end:

• Clip Low — Luminance values below this are fully transparent (black in the matte). This is the primary keying control — raise it to remove dark areas.
• Clip High — Used to remove bright areas from the trails. Luminance values above this are fully transparent (black in the matte).
• The respective softness controls soften the hard edges of the clips.

Softness Low / Softness High

Smooths the hard edges of the clip points using a smoothstep function. Higher softness = gentler transition. This prevents harsh matte edges that can create artifacts in the trail.

View Alpha

Turn this on to see the matte as a grayscale image in the viewer. White = included in trail, black = excluded. Essential for tuning the luminance keyer — adjust Clip Low/High and Softness until the matte looks right, then turn View Alpha off.

Premultiply Source

When enabled (default), the source RGB is multiplied by the computed alpha before entering the trail pipeline. This removes the original background from transparent areas, preventing it from leaking through when the trail is composited downstream. You'll almost always want this on.

Use First Frame as Background

When enabled, the full source image (including background) is used as the starting frame for the trail. When off (default), the first frame is the matted foreground over black — only the keyed subject seeds the trail.

Generate Alpha Output

When enabled (default), the effect outputs an alpha channel that accumulates and decays along with the trail. This allows the trail to be composited over other layers in the timeline, or over other elements in Fusion, Flame, or Nuke.

Tips & Tricks

Classic Video Feedback Tunnel

1. Set Zoom to 1.01-1.02
2. Set Rotation to 30-180 degrees
3. Set Feedback Amount to 1.0
4. Play forward and watch the spiral form
5. Move the Transform Center to steer the tunnel
6. Change the Rotation, Zoom, Saturation Boost and Hue Shift.
7. Enjoy!

Rainbow Motion Trails

1. Set Hue Shift to 5-10 degrees
2. Set Feedback Amount to 0.95-1.0
3. Set Strobe Interval to 1
4. Move something across frame — each echo is a different changing color.
5. Try using negative numbers in the hue shift, to get different color distributions.

Smoky / Atmospheric Trail

1. Set Blur to 2-5
2. Set Feedback Amount to 0.98
3. Set Shift Y to 0.005
4. Add Swirl Strength of 1-2
5. Set Swirl Speed to 0.3-0.5
6. Set Swirl Frequency to 2
7. Set Luma Expand to 6
8. The trail dissolves into drifting smoke

Psychedelic Wallpaper

1. Set Strobe Interval to 8-15
2. Set Zoom to 1.005
3. Set Rotation to 0.5-1 degree
4. Set Hue Shift to 3-5 degrees
5. Add Swirl Strength of 1-2
6. Let it cook — the image builds into abstract, evolving patterns

Troubleshooting

Trail doesn't appear / only see current frame

• You need to play forward from the beginning of the clip. This is a temporal effect that builds up over time. Scrubbing or jumping to a frame won't show accumulated trails. Scrubbing forward won't show the trails correctly, and scrubbing backwards will show incorrect trails, or none at all.

Trail clears when I stop and restart playback/trail clears randomly in renders.

• In Resolve, set Playback → Render Cache to None or User. The "Smart" cache renders frames out of order, which is incompatible with temporal accumulation effects.

Black borders creeping in at edges

• Enable Wrap Offsets to wrap the trail at frame edges instead of going to black.

Trail evolves too fast / too slow

• Feedback Amount is the primary decay control. Values close to 1.0 (0.98-0.99) produce long-lasting trails. Lower values (0.9-0.95) make trails fade faster.
• Strobe Interval controls how often new source is stamped. Higher values = more pure trail evolution between stamps.
• If you're referring to the swirling effect being too fast, try lowering Swirl Strength, and swirl speed.

Keyer isn't isolating my subject

If you're using Magic Mask: You need to mask the subject in a separate node, not the one that has the ofx attached. Then, connect the BLUE output of the Magic Mask node to both the second GREEN AND BLUE inputs of the corrector with the ofx attached. (If you're having trouble with Magic Mask itself, there are many good tutorials on youtube.)

If you're using the internal luminance keyer: You have to understand that unless your subject is shot over black, you're not going to get a perfect isolation of your subject; Even if you're subject is over black, the dark areas of your subject will be transparent. But - you can optimize what you have:

• Turn on View Alpha to see the matte.
• If using Luminance Key, adjust Clip Low and Clip High to bracket your subject's luminance range.
• Add Softness to smooth harsh matte edges.
• Try Invert if your subject is dark on a bright background.

I've made an effect with alpha enabled - but I don't see it composited over the background layer in the timeline after I "render in place".

• When you render in place, switch to a format that supports an alpha channel - like Prores 4444 .