Radial Length Helper (WAN) — ComfyUI Custom Node

A tiny helper node for WAN + RadialAttention workflows. It snaps Width / Height / Length to valid values and shows a compact list of valid temporal lengths.

• Models: WAN 14B (stride /16) and WAN 5B (stride /32)
• Inputs: model_kind, width, height, length
• Outputs: L_snapped, W_out, H_out
• UI: compact readout with snapped spatial, snapped length, and valid L in 1..200 (max 4 rows, ellipsis if long)
• Optional: a frontend JS overlay for live, in-node updates while scrubbing (10px font)

---

What the node does

• Snaps Width/Height to the nearest multiple of the model’s stride
  (14B → /16, 5B → /32).
• Computes the temporal congruence so tokens % 128 == 0, where
  tokens = (W/stride) * (H/stride) * ((L+3)/4) with integer (L+3)/4.
• Snaps Length L to the nearest valid value from that progression.
• Displays a compact readout in the node (and live if overlay is installed):
  • spatial: W_in×H_in → W×H (/ stride)
  • L snapped: …
  • valid L (1..200): N vals followed by up to 4 wrapped rows (ellipsis in the middle if long)

---

Math details (reference)

• stride = 16 for WAN 14B, stride = 32 for WAN 5B.
• A = (W/stride) * (H/stride).
• tokens = A * T' where T' = (L+3)/4 must be an integer.
• We want tokens % 128 == 0 → an arithmetic progression on L:
  • g = gcd(128, A)
  • m = 4 * (128 / g)
  • r = (m - 3) mod m
  • Valid lengths: L ≡ r (mod m)
• The node snaps the requested L to the nearest valid value.

---

Example wiring

[Radial Length Helper (WAN)]
   ├─ L_snapped  →  [EmptyHunyuanLatentVideo.length]
   ├─ W_out      →  [EmptyHunyuanLatentVideo.width]
   └─ H_out      →  [EmptyHunyuanLatentVideo.height]

---

Version notes

• Works with ComfyUI Windows Portable (Python embedded ok).
• Independent of torch/CUDA; the node itself has no native deps.
• Overlay uses Comfy’s app.registerExtension hook (no extra packages).

---

License & credits

• MIT (or your preferred permissive license).
• Thanks to the EA Motion Bias node for the UX pattern (live overlay, compact readout).