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Expression

Expression · screenshot coming soon

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What this node does

Expression evaluates a math expression over time and outputs a keyframe track (COMFYTV_TEXT). You write something like sin(t*2)*10 or noise(t*2)*20, pick which field it drives, set the sample rate and duration, then it samples the curve. The card draws a live preview graph of the curve as you type (debounced, with an error message if the expression is invalid). Press ▶ Run to emit the keyframes. The expression is evaluated in a safe sandbox: only numeric literals, arithmetic/comparison/boolean operators, the built-in variables, and the built-in functions are allowed (no attribute access, no keyword args, max 2000 chars).

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Variables and functions you can use

  • Variables: frame, t (seconds), duration, fps, plus constants pi, e.
  • Functions: sin cos tan asin acos atan atan2 exp log sqrt pow abs floor ceil round min max sign degrees radians; steps/interpolation boxstep linearstep smoothstep gaussstep remap mix clamp; and noise noise snoise fbm turbulence cellnoise pnoise cellnoise random hash. The seed parameter seeds the noise/random functions.

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When to use it

  • Add organic wobble to a parameter (noise(t*3)*5) instead of hand-keying it.
  • Drive a cyclic motion (sin(t*2)*30) for a bob, sway, or pulse.
  • Generate a ramp or eased curve to feed an FX stage’s keyframe input.

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Parameters

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expression

The math expression to evaluate. Default sin(t*2)*10. Uses the variables/functions above.

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field

Which animation field the curve targets: v, scale, opacity, x, y, rotation. Default v. This is the key name written into the output track.

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rate

Keyframes per second sampled from the curve, 1–60, default 10. Higher = smoother track, more keys.

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duration

Curve length in seconds, 0.05–3600, default 5. If a video is wired, its real duration overrides this (and the card hides the Duration slider).

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fps

Frames per second used to compute the frame variable, 1–120, default 24. A wired video’s real fps overrides this.

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seed

Seed for the noise/random functions, 0–99999, default 0. Change it for a different random pattern.

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Inputs and outputs

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Tips

  • Wire a video to lock the curve to that clip’s exact duration and fps — the Duration slider disappears when a video is connected.
  • Raise rate for smoother, denser keys on fast-moving curves; lower it for lighter tracks.
  • Only the listed names are allowed — an unknown name, keyword argument, or non-numeric constant makes the expression error (shown in the preview).
  • t is seconds and frame is t*fps; use whichever your expression reads more naturally.

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Types and bridges

COMFYTV_TEXT / COMFYTV_VIDEO are ComfyTV project snapshots, not native ComfyUI types. Use a Bridge (ComfyTV/Bridge) to interoperate with native nodes. See bridges.md.
  • FX Chain — bakes the FX chain whose parameters an expression track can animate.
  • Any ComfyTV VideoFX stage that accepts a keyframe track.