arkennemasis Scene At (one scene of the plan, by index)

ComfyUI has no loop construct, but it does have an executor that already iterates: a node that declares list outputs makes every downstream node run once per item. That's ArkSceneList's trick for fanning a shot plan out. ArkSceneAt is the opposite move - it picks one scene out of the plan by index and returns it as plain values, so you can build a per-scene chain that renders, saves and frees memory before the next scene begins.

Why would you want the single-scene version when the list version exists? The description answers it: "use it inside a for-loop so each shot renders, saves and frees before the next begins - which is what lets a folder of any size finish." If a video pipeline tries to hold every scene in flight at once, a folder of any real size runs out of VRAM long before it runs out of scenes. One scene at a time, resources returned between iterations, and the size stops being a problem.

How it works

Give it scenes_json (the array from the story agent) and an index (0-based - wire the loop's index in), and it returns that scene's fields: video_prompt, voice_text and image_prompt, plus scene_number and total. The field parsing is deliberately tolerant - it accepts camelCase or snake_case for the same field, so a plan written one way doesn't produce a silent empty string three nodes later. Out-of-range indexes clamp to the nearest valid scene with a console note. IS_CHANGED returns NaN so it never serves a stale cached scene across iterations.

Inputs and outputs

• scenes_json - the JSON array from the story agent.
• index - 0-based; wire the loop's index here.
• video_prompt, voice_text, image_prompt - the three text outputs for the generation chain.
• scene_number, total - position and count, handy for filenames, logs, or "scene 3 of 12" overlays.

In the arkennemasis video pipeline these feed the per-shot chain: condition → sample → decode video and audio → mux → save → free. ArkQwenTTS can supply the voice for voice_text, and ArkRunLog can record each scene as it completes.

Install and gotchas

Part of the arkennemasis pack:

cd ComfyUI/custom_nodes
git clone https://github.com/Hishamahmer/comfyui-arkennemasis
pip install -r ComfyUI/custom_nodes/comfyui-arkennemasis/requirements.txt

Restart, or install via ComfyUI Manager by repo URL.

An empty or unparseable plan returns empty strings and a console warning rather than crashing - which is friendly, but it means an empty scenes_json won't fail loudly. Check the console if a loop "completes" with nothing produced. And remember the pairing: ArkSceneAt is the per-index picker for the loop style, ArkSceneList is the fan-out for the list style. Pick the one that matches how your canvas is wired; mixing both against the same plan is the only way to confuse yourself.