H3 Relay · Sequence Start

H3 Relay · Sequence Start is the front door to the whole pack. It defines the run: the name, the global prompt, the native H3 frame size, the continuation-overlap contract, and the sampler/scheduler/Spectrum pairing that every shot in the movie inherits. Its sequence output is what feeds the first Generate Shot, and from there the chain runs shot after shot until you hit Assemble. Nothing happens before this node, and it's the one node you will genuinely configure by hand.

Here's the mental model: MiniMax H3 generates 4–15 second clips with natively synced audio, and H3 Relay turns that into long-form video by chaining shots - each continuation carries sliding visual/audio history from the accepted previous shots. This node sets the rules for that whole process and stamps the run's identity on disk (content-addressed records live under ComfyUI's protected user/__h3_relay_cache).

The inputs you'll actually set

• run_name (default h3_relay_movie) - your run's identity. This is the key to the entire resumability story: same name + same inputs = cache hits; new name = fresh run. Name it something meaningful.
• global_prompt (multiline) - the story-level prompt every shot inherits. Shot-specific prompts get layered on top in Generate Shot.
• width / height - default 832x480, the native H3 review tier. Step of 32.
• h3_overlap_frames - the sequence-wide continuation history: 18, 35, 52, or 69 frames (default 18). H3's sliding history lives on a 17k+1 temporal grid, so those are your only choices. Bigger overlap carries more visual/audio context into each continuation but shortens each shot's delivered duration. Start at 18.
• sampler - the complete native ComfyUI sampler list, default euler. Mix freely.
• scheduler - the complete BasicScheduler list plus beta57, which is H3 Relay's addition: the exact manual H3 curve at 16 steps, falling back to alpha 0.5 / beta 0.7 otherwise. beta57 is the default for a reason.
• spectrum_enabled (default true) - turns the Spectrum smoothing layer on independently. Supported single-call samplers are Euler, res_multistep variants, and ER-SDE; other samplers just run with Spectrum bypassed.

The default pairing - Euler + beta57 + Spectrum - is the validated configuration. Change it because you have a reason, not because you're curious.

Outputs

• sequence (H3_RELAY_SEQUENCE) - the run's continuation state, wired into Generate Shot. This is the native H3 stream; LTX/interp/assembly live on the separate enhanced wire.
• status (STRING) - a human-readable summary of what the node decided, including your sampler/scheduler/Spectrum choices.

The gotchas that bite

The h3_overlap_frames check is hard: pass a value outside {18, 35, 52, 69} and the node raises rather than silently using a broken grid. And note that deviating from the default pairing (or the default overlap) changes the run's generation_fingerprint - that's deliberate, and it means those runs cache separately from defaults, which is correct but surprising if you expect a "minor tweak" to reuse results.

For install: ComfyUI Manager → search H3 Relay → install → restart, or git clone https://github.com/akatz-ai/h3-relay into custom_nodes. You'll still need the MiniMax H3 models from MODELS.md (FL2VA/Ref2VA, the Qwen3-VL 32B encoder, video + audio VAEs), FFmpeg on PATH, and - worth repeating because the weights are separately licensed from the pack's GPL-3.0 source - the H3 Community License excludes the US, EU, UK, and Korea. Check your territory before you commit to a 58-second Spectrum-16 run.