FadeMixer

A small After Effects ExtendScript (.jsx) that adds Stereo Mixer fade in / fade out keyframes to selected layers in one click.

What it does

• Adds the Stereo Mixer effect to each selected layer (if not already present).
• Animates the Left and Right channel inputs from 0 → 100 (fade in) at the layer's in-point and 100 → 0 (fade out) at the out-point.
• Applies temporal easing for smooth fades.
• Configurable fade length (in frames) and toggles for fade-in / fade-out.
• Wraps everything in a single undo group.

Usage

1. Copy FadeMixer.jsx into your After Effects Scripts (or Scripts/ScriptUI Panels) folder.
2. In AE: File → Scripts → FadeMixer.jsx (or open it as a docked panel from Window → FadeMixer.jsx).
3. Select one or more layers in the active composition.
4. Set the fade length, tick Fade In / Fade Out, and click Apply Stereo Mixer Fade.

Requirements

• After Effects (any reasonably recent version that supports the Stereo Mixer effect and ScriptUI panels).
• Allow scripts to write files / access network is not required.