H3 Reference Isolate

In H3, your text prompt and references sit at the front of one big sequence, and attention is a square: the prefix attends to the video being denoised, even though nothing downstream ever reads that part of its output and its timestep never moves. It's pure wasted work - and it's the only way the references can drift, since reading the noisy target is all that perturbs them. H3 Reference Isolate stops that: one square attention becomes two rectangular ones. The generation still sees its references in full; the references just stop watching the noise.

How it works

model in, MODEL out, patched. The saving scales with how much of the packed sequence is references - measured 25% with a full-res video reference, 1.3% with none - and it costs no memory. That's the honest scope: on a plain text-to-video clip there's almost nothing to save; on a high-resolution, multi-reference edit, it's a real cut.

Two inputs beyond the model:

• start_percent (default 0) - where isolation switches on. Above 0, the references watch the early steps - where composition is decided - before being frozen. The tooltip says it plainly: raise this first if identity or layout drifts.
• end_percent (default 1) - where it switches off. 1.0 keeps it on to the end.

When to reach for it

Use it on reference-heavy work - image, video or audio references driving an edit - where the prefix is a meaningful fraction of the sequence. Skip it for plain clips; the 1.3% saving is noise. One interplay to know: it does what H3 Sliding Window's isolate_references toggle does, but they can't run together - if you're on Sliding Window, use its built-in toggle instead of this node. And when the reference's identity is the fine detail you're chasing, the early-steps-watching behavior of a nonzero start_percent is your lever: let composition settle, then freeze the references for the refinement pass.

Install

Pack install: ComfyUI Manager → "Nynxz H3", or:

cd ComfyUI/custom_nodes
git clone https://github.com/Nynxz/ComfyUI-NynxzH3

Restart. Pure Python, no dependencies, ComfyUI 0.30.0+.

The one-liner

Chain it in before the sampler on reference-heavy edits, leave start_percent at 0, and if identity starts wandering, raise that knob before you blame anything else. On a plain clip it's not worth your canvas space - it needs references to have anything to do.