🔗 H3 Relay · Chain

Multi-segment generation with the H3 Latent Relay pack has one real chore: run_id and stage_index have to match across the Latent Save, the Copy Bridge, the Latent Load, Trim AV, Audio Seam, and this node - six places. The pack's canvas JS does auto-sync run_id within a group, but the stage number is still something you have to bump between runs. Do it by hand for a ten-segment piece and you will eventually do it wrong, and the failure mode isn't a crash; it's a segment silently continued from the wrong tail.

H3RelayChain is the controller that takes that job. It's plumbing, in the truest sense from the node plumbing layer - it carries no pixels, no latent, no audio. It finds the Copy Bridge, Latent Save and Latent Load in its group, advances their stage numbers, and queues the next run for you. It also has a prompt output, which is how per-segment wording works.

What you actually get

The node is mostly buttons. ▶ Run queues the current stage. ✔ Approve bumps the stage and queues the next. ⏩ 连跑 (run-through) walks segments stages automatically - set segments: 0 and it keeps going until you hit stop. ↺ Reset takes you back to stage 0. 🧩 拼成一条 (concat into one) stitches the segments you've already rendered into a single film, using the pack's own /h3relay/concat route on the backend.

Two conveniences, both off by default so old graphs don't shift:

• prompts - paste every segment's text separated by a line containing only ---. Block 1 goes to segment 0, block 2 to segment 1, and so on, selected by stage_index. Wire the node's prompt output into your prompt encoder's prompt input - that's the step people miss. The block count is checked against segments: run short and it refuses to queue and tells you, rather than silently reusing the last block. That refusal is on purpose. A silent reuse means you render three segments of identical action and only notice at the join.
• auto_concat - with run_id set, each finished segment records its progress to _progress.json in the segment folder, so the run-through resumes from where it died after a crash or restart.

Required input is just segments. Useful optional: run_id (needed for skip-proof, and must match the bridge/save), stage_index, prompts, auto_concat, concat_name, audio_out (aac_256k default, pcm_lossless if you're handing this to an edit, though that one has no browser preview audio), video_crf (only matters when segments mismatch and a re-encode is unavoidable). The status and concat_result fields are outputs dressed as widgets - don't type in them.

Outputs are prompt (the per-stage text) and report.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/ZenHG/ComfyUI-H3-Latent-Relay.git

ComfyUI Manager → search h3-latent-relay also works. Restart the backend afterwards. Base deps come from ComfyUI itself; concatenation additionally needs av>=17 (already there). The buttons are front-end JS inside the pack's web/ folder, so if a click does nothing, refresh the browser tab as well as restarting Python.

Traps

Group the nodes. The controller looks for the bridge, save and load inside its own group box - select Chain + Copy Bridge + Latent Save + Latent Load, right-click, add to a group. Ungrouped it falls back to whole-graph scope and warns about it. If you've changed run_id and one node didn't follow, it's almost always a node outside the group.

Button-operated means API submissions ignore the buttons. This node is honest about that boundary: the pack's rule is that every feature must be reachable both from the canvas and from an API-submitted graph. Here the prompt dispatch was moved into the node itself so both paths share one implementation, but stage advancement is genuinely a canvas gesture - submitting the graph JSON means your loop advances stage_index yourself. The pack's docs ship a loop template for that.

segments counts, prompts blocks must cover it. Set segments: 5 with three prompt blocks and you get three renders and a refusal, not five.

Not the same as a sampler chain. If you're looking for the "chain" that controls sampling steps, that's a different node entirely. This one only sequences stages of a film.