H3 Edit Duration — 24 FPS

H3 Edit Duration - 24 FPS is a two-line utility with an opinion: if you're doing an H3 video edit, the source video you load and the duration your story director plans for had better be the same duration, or nothing lines up. This node exists to make that impossible to get wrong. You type one number, and it hands you the two values that keep H3 Story Director and VHS Load Video on one exact clock.

It's the kind of node you barely think about - until the alternative is manually computing frame_load_cap in your head and discovering your source clip is two frames off, and every prompt the Director writes is planning against the wrong length.

How it works

The mechanism is arithmetic, and it's honest about it. You enter a duration_seconds value and the node converts it to a frame count at exactly 24 fps: frame_load_cap = round(duration_seconds × 24). Then it checks that the rounded result is actually a whole frame - because if your duration doesn't resolve cleanly at 24 fps, the node throws a clear error instead of silently feeding VHS a cap that produces a mismatched clip. Set it in 0.5s steps and you're safe; try something like 2.1 seconds and you'll get told exactly why that's 50.4 frames and unacceptable.

The inputs and outputs

One input, and it's the one you'll ever touch:

• duration_seconds - 5.0 by default, 0.5 to 15.0, stepped in 0.5. The requested source-video duration at exactly 24 fps.

Two outputs, and the tooltips tell you exactly where they go:

• duration_seconds (FLOAT) - connect to H3 Story Director's scene_duration_seconds.
• frame_load_cap (INT) - connect directly to VHS Load Video's frame_load_cap.

That's the whole graph move: one node feeding the Director's duration and VHS's frame cap from a single source of truth. Change the number once and both sides follow.

Install

It's part of the Vision Prompt Assistant pack. ComfyUI Manager → search Vision Prompt Assistant, or:

cd ComfyUI/custom_nodes
git clone https://github.com/elgalardi/ComfyUI-VisionPromptAssistant

Restart ComfyUI and you'll find it under the conditioning/minimax category. No extra dependencies, no model files - it's a pure utility.

Common issues

There's basically one failure mode, and it's by design: the "must resolve to a whole frame at 24 fps" error when you pick a duration that lands mid-frame. Either bump it to the nearest 0.5s step or accept that VHS is going to round. Everything else about this node is a wire and two numbers.

Pair it with the H3 Story Director's draft_only flow - get the duration right first, then spend the API call planning, and you won't be re-running the Director because your source clip came out 0.04 seconds shorter than the plan assumed.