FL Audio Reactive Edge Glow

A rim-light effect that breathes with the music: this node finds edges in your frames (or uses edges you already computed) and adds a colored glow along them, with the glow's intensity modulated by an audio envelope. It's the kind of look you see in a lot of edited music-video/VJ content - cheaper, more controllable, and more predictable than trying to coax a diffusion model into producing the same thing.

How it works

Edge detection is Sobel-based - a classic gradient operator that finds sharp transitions in the image and treats them as edges. You can either let the node compute those edges itself from frames, or supply your own pre-computed edge_frames if you already have cleaner or differently-styled edges from elsewhere (a ControlNet preprocessor's output, for instance). Once it has edges, it adds a glow along them using your chosen glow_color and blend_mode, with the glow's strength coming from two combined sources: a constant glow_intensity and an audio-envelope-driven envelope_intensity on top of it.

The inputs and outputs that matter

Required: frames, envelope_json.

Optional: edge_frames - bypass the built-in Sobel pass entirely with your own edges; edge_threshold (0–1, default 0.1) - how strong a gradient counts as an edge (lower catches more/fainter detail, higher restricts glow to only the strongest outlines - has no effect if you supplied your own edge_frames); glow_intensity (0–2, default 0.5) - the base, non-reactive glow strength; envelope_intensity (0–2, default 0.3) - how much the audio envelope adds on top of that base; glow_color (white/original/cyan/magenta/yellow, default cyan - original keeps each edge's own source color instead of tinting it); blend_mode (add/screen/overlay, default add - add is the brightest and most literal glow, screen softer, overlay leans into midtones).

Output: frames.

How to install it

ComfyUI Manager: search ComfyUI_Fill-Nodes, install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/filliptm/ComfyUI_Fill-Nodes

then restart. No extra dependency for this node beyond standard image math - the audio side of the pipeline (drum detection, envelope generation) lives in separate upstream nodes.

Common issues & troubleshooting

No visible glow at all. Check that edge_threshold isn't set so high that Sobel finds essentially nothing on your source - this effect needs real contrast/detail in the frame to find edges in the first place. A flat, soft, low-contrast source gives a flat, glow-less result no matter how far you push glow_intensity.

Glow is constant, doesn't pulse with the music. glow_intensity alone gives a static glow with zero reactivity. envelope_intensity is what actually ties the effect to the beat - if it's at 0, you'll get glow with no pulse regardless of how strong envelope_intensity's cap is set.

Custom edge_frames don't seem to matter. Remember supplying edge_frames bypasses the internal Sobel pass entirely, which means edge_threshold has no effect in that mode - if you're tuning edge_threshold and nothing changes, you've probably left edge_frames connected from an earlier experiment.