MotionTrails

Blackmagic places Motion Trails in Resolve FX Temporal and marks it Studio Version Only. It copies the image to create ghost-like trails on moving imagery and can simulate long-shutter-style echoes or analog-video feedback.

Trail Length and Dropoff are the foundation. Trail Length determines how many copies participate. Dropoff applies compounded fade: Blackmagic's example at 0.5 produces roughly 50%, 25%, 12.5% and so on. Therefore values closer to 1 preserve more energy in older copies and make the trail denser; they do not make it disappear faster.

MotionTrails differs from MotionBlur. MotionBlur estimates movement and attempts a continuous motion-aware smear. MotionTrails keeps discrete frame copies, so fast motion reads as afterimages or echo states that can then be transformed further.

With Reuse Current Frame off, each successive copy comes from temporal history: the first copy uses current-1, the second current-2 and so on. With Reuse Current Frame on, every copy uses the current frame and separation is generated by Move Trail, turning the effect into a graphic repeat/feedback generator.

Move Trail is cumulative from copy to copy. Blackmagic's documented example is Rotate = 5 degrees: the first copy is rotated 5 degrees, the second 10 and the third 15. Small Pan, Zoom and Rotate values can therefore become pronounced across a long Trail Length.

Pan sets the per-copy offset magnitude, Pan Angle sets its direction in degrees, Zoom applies successive scaling and Rotate applies successive rotation. These controls transform trail copies rather than upstream source geometry. With Pan at zero, Pan Angle alone has no meaningful displacement to direct.

Composite Gamma controls how overlapping copies combine in brightness. Timeline follows the timeline color-space context, Rec.709 uses Rec.709 Gamma 2.2, Linear uses linear gamma and often produces stronger highlights, while Custom exposes a separate Custom Gamma control. The manual states a default of 2.4 and that Custom Gamma = 1.0 is equivalent to Linear.

The bundled Fusion capture shows Timeline / Rec.709 / Linear / Custom in the Composite Gamma menu but not the conditional Custom Gamma slider because Timeline is selected. The conditional control is included from the Resolve 21 manual rather than pretending each menu option is a separate parameter.

The current Resolve FX chapter also documents an Input Alpha branch for the general Motion Trails effect, while the captured Fusion 21 Inspector on this page instead shows Use Key / Mask Input and does not show Input Alpha. Input Alpha is therefore not counted as an authored control for this Fusion page without separate target-build confirmation.

Use Key / Mask Input is confirmed by the captured Fusion Inspector and is associated with the separate blue key/mask input. The reviewed prose manual does not define the exact Fusion-specific pre/post evaluation order relative to temporal copies, so this page treats that order as a live-verification boundary rather than assuming ordinary post-effect-mask semantics.

Border Type determines what appears beyond the original frame after trail transforms: Black leaves black, Replicate extends edge pixels, Reflect mirrors the image and Wrap-Around brings content around from the opposite side.

Soften is not a general blur for the whole trail. Blackmagic describes it as blending the rectangular frame borders of the trail copies so they feel less mechanical. Judge it where transformed copy boundaries are actually visible.

The effect is temporal. A single visible Image Input still implies neighboring-frame reads when Reuse Current Frame is off. Inspect clip starts, edit boundaries, retimes and discontinuities separately because history may not behave like the middle of a continuous shot.

A robust workflow is to establish Trail Length and Dropoff with Move Trail neutral, decide whether copies use real history or the current frame, then add Pan/Zoom/Rotate, choose Composite Gamma and finally solve Border Type/Soften and key/mask behavior.