> ## Documentation Index > Fetch the complete documentation index at: https://comfytv.org/llms.txt > Use this file to discover all available pages before exploring further. # Expression > Turn a math expression into an animation curve — a per-frame value track you can drive an FX parameter with, like a Nuke/AE expression or a wiggle. Expression ## 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). ### 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. ## 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. ## Parameters ### expression The math expression to evaluate. Default `sin(t*2)*10`. Uses the variables/functions above. ### 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. ### rate Keyframes per second sampled from the curve, 1–60, default 10. Higher = smoother track, more keys. ### 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). ### fps Frames per second used to compute the `frame` variable, 1–120, default 24. **A wired video's real fps overrides this.** ### seed Seed for the noise/random functions, 0–99999, default 0. Change it for a different random pattern. ## Inputs and outputs | Slot | Type | Meaning | | ------------------- | --------------- | -------------------------------------------------------------------- | | **video** (in) | `COMFYTV_VIDEO` | Optional; if present, its duration and fps override the sliders | | **keyframes** (out) | `COMFYTV_TEXT` | The sampled keyframe track (`{t, , interp:"linear"}` per key) | ## 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. ## 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](https://github.com/jtydhr88/ComfyTV/blob/main/docs/bridges.md). ## Related nodes * **FX Chain** — bakes the FX chain whose parameters an expression track can animate. * Any ComfyTV **VideoFX** stage that accepts a keyframe track.