How does video feedback work?

A camera looks at a screen showing its own output, so each frame contains a processed copy of the previous frame. Zoom, rotation, and brightness changes accumulate through the loop and turn into spirals and tunnels. The process is sensitive to small changes, so two runs of the same setup rarely match exactly, which is part of its appeal.

Who made video feedback an art form?

Video artists and engineers in the 1960s and 1970s explored it with cameras, monitors, and early synthesizers, treating the loop as a visual instrument. Many of today's glitch and VJ looks trace back to those experiments. Hardware like keyers, colorizers, and scan converters was later added to the loop to control the patterns more precisely.

Why do feedback patterns look different from a simple echo?

An echo only mixes a few delayed copies of the source. Feedback recirculates its own output, so the image processes itself indefinitely, and the nonlinearity of the loop creates new structure that was never in the source. The amount of recirculated signal is the key, and tiny adjustments to it separate a calm tunnel from a violent storm.

Why does my feedback fill the screen with white?

The loop gain is above one, so brightness grows on every pass until it saturates. Lower the amount of feedback, increase the decay, or darken the loop so the brightest areas do not accumulate. A gentle clip or a darker input also helps, because it removes the bright seed that the loop would otherwise amplify.

Video feedback: what it is and how to make it in After Effects

Video feedback is the recursive pattern made when a camera films a screen showing its own output. See how the loop works and how to build it in After Effects.

WHAT CAUSES IT

Video feedback is the recursive picture produced when a video output is routed back into the video input that creates it, most simply by pointing a camera at a monitor that displays that camera's signal. Each trip around the loop takes about one frame time, because the camera scans the monitor, the signal is processed, and the monitor draws it. The image on the screen is therefore a smaller or rotated copy of the previous frame, containing a copy of the frame before that, and so on, producing a tunnel of nested images. The look is governed by the loop gain, the lens zoom and rotation, the brightness and contrast controls, and the delay. If the gain is below one, the pattern fades to a steady state. If it is above one, bright areas grow until the camera saturates, and the nonlinearity of the sensor and the monitor turns small disturbances into spirals and fractal swirls. Phosphor persistence and camera lag add trails that smear motion along the path of the loop.

WHAT IT LOOKS LIKE

A receding tunnel or spiral of repeated frames, each smaller and rotated slightly from the one before, often with colors that shift as they recede. Small movements of the camera or a hand in the frame make ripples and arms of light grow out of the center. Bright areas bloom into glowing structures, and dark areas stay quiet until a disturbance reaches them. When the loop is stable the pattern holds still, and when it is not, it boils and evolves unpredictably. Fast motion leaves long streaking trails that curl along the spiral.

WHERE YOU SEE IT

Experimental video art from the 1960s and 1970s, music videos, television title sequences of the 1970s and 1980s, and VJ visuals. It is also a classic tool of video synthesis, where artists used a camera and a monitor as an analog computer. In modern editing it is used for psychedelic transitions, dream sequences, hacked broadcast moments, and any scene where a screen watches itself.

RECREATE IT

ECHO PARASITE

CONTROLS LIVE LOOP, ECHO SCALE, ECHO DECAY, ECHO

LIVE LOOP feeds the output back into the input for true recursion, so start there. Use ECHO SCALE to set how much each pass is shrunk or grown, which defines the tunnel, and ECHO DECAY to control how quickly the pattern fades. Keep the loop gain gentle at the beginning; a runaway loop fills the frame with white. ECHO adds simple delayed copies when you do not need full recursion.

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SEE ECHO PARASITE

HOW TO MAKE IT IN AFTER EFFECTS

1. Place your source footage in a composition and pre-compose it. 2. Apply ECHO PARASITE. 3. Turn on LIVE LOOP and start with a small amount of ECHO SCALE, so each pass shrinks the picture by a little. 4. Adjust ECHO DECAY until the tunnel holds for several repeats and then fades. 5. Play the composition from the beginning, since feedback depends on the frames that came before; scrubbing in the middle of the timeline may not show the final look until the history has built up. 6. To make a spiral instead of a straight tunnel, add a small amount of PARASITE WARP. 7. Keyframe ECHO SCALE gradually to zoom the tunnel in or out. 8. Use a dark background with bright shapes for the clearest result. 9. When the look is right, render the sequence from the start to avoid history differences between preview and final output.

QUESTIONS

How does video feedback work?: A camera looks at a screen showing its own output, so each frame contains a processed copy of the previous frame. Zoom, rotation, and brightness changes accumulate through the loop and turn into spirals and tunnels. The process is sensitive to small changes, so two runs of the same setup rarely match exactly, which is part of its appeal.
Who made video feedback an art form?: Video artists and engineers in the 1960s and 1970s explored it with cameras, monitors, and early synthesizers, treating the loop as a visual instrument. Many of today's glitch and VJ looks trace back to those experiments. Hardware like keyers, colorizers, and scan converters was later added to the loop to control the patterns more precisely.
Why do feedback patterns look different from a simple echo?: An echo only mixes a few delayed copies of the source. Feedback recirculates its own output, so the image processes itself indefinitely, and the nonlinearity of the loop creates new structure that was never in the source. The amount of recirculated signal is the key, and tiny adjustments to it separate a calm tunnel from a violent storm.
Why does my feedback fill the screen with white?: The loop gain is above one, so brightness grows on every pass until it saturates. Lower the amount of feedback, increase the decay, or darken the loop so the brightest areas do not accumulate. A gentle clip or a darker input also helps, because it removes the bright seed that the loop would otherwise amplify.

RELATED EFFECTS

Rescan Rescan is the look of a camera filming a CRT screen: refresh bars, moire and soft glow. Learn what it does to a picture and how to build it with ECHO PARASITE.
Ghosting Ghosting is the faint offset duplicate image seen on analog TV. Learn how signal reflections cause it and how to build it with ECHO PARASITE in After Effects.
CRT scanlines CRT scanlines are the dark gaps between the lit lines of a tube display. Learn how the beam makes them and how to build them with WIRE WRAITH in After Effects.

LOOKS THAT USE IT

video feedback tunnel look The video feedback tunnel look: infinite spiraling echoes from a camera aimed at its own monitor, recreated in After Effects with loop and decay.
Rutt-Etra scan look The Rutt-Etra scan look: video displaced into glowing raster lines by brightness, as on the 1972 scan processor, built in After Effects with Wire Wraith.
analog horror look The analog horror look: broadcast and VHS signal failure as dread, with static, tracking loss and color collapse, built in After Effects.