SAX MiniMax H3 Sampler

Why this node is the missing middle

MiniMax H3 workflows split into three acts. The loader hands you models. MiniMaxH3-Director (a separate pack) does the interesting part - prompt, latent, conditioning, sigma shift - and spits out model, positive and latent. And then... you're supposed to build the other half of the graph yourself: RandomNoise → KSamplerSelect → BasicScheduler → BasicGuider → SamplerCustomAdvanced, then decode video through the video VAE, decode audio through the audio VAE, and finally CreateVideo to get something you can save.

That's eight core nodes of pure plumbing, and every one of them is a place to wire the audio VAE into a video socket and wonder why the output hisses.

SAX MiniMax H3 Sampler is those eight nodes as one. It takes the Director's output, samples it, decodes both modalities, and hands you a VIDEO. The whole H3 pipeline becomes four nodes:

SAX MiniMax H3 Loader → MiniMax H3 Director → SAX MiniMax H3 Sampler → Save Video

How it works

The node reads what it can from the PIPE: the video VAE, the audio VAE, the seed, and the loader's steps / sampler_name / scheduler settings. Then it runs ComfyUI's own core sampler path rather than reimplementing H3 - which is the right call, because it means ComfyUI fixing H3 internals fixes this node too.

Two details of that path matter:

• There's no CFG, because there's no negative. Guidance goes through BasicGuider with the Director's positive alone, which is H3's official setup (the equivalent of cfg=1). Don't go hunting for a negative prompt here - the Director owns that side of the graph.
• Video and audio decode from the same joint latent, each through its own VAE. That's the whole point of H3: audio isn't a second pass bolted onto a silent generator, it comes out of the same sampling run. denoise is pinned at 1.0, fps is the one thing you can touch.

Inputs that matter: pipe from the H3 Loader; model (the Director's patched model - this is the one carrying the sigma shift, not the raw loader MODEL); positive (Director); latent (Director); and the optional fps, default 24.

Outputs: PIPE (now carrying samples and the decoded images, plus the actual clip_width / clip_height), VIDEO, IMAGE (the frame stack, handy for a preview or a second pass), AUDIO. Wire VIDEO into core Save Video, or into the pack's own SAX Output if you're staying in the family.

There is no steps widget, and that's fine

The most common "the node is broken" moment with the sampler is that it has almost no widgets. steps, seed, sampler_name and scheduler_name aren't here - they travel on the PIPE from the Loader, which is the point of the pack's pipe pattern: set them once, upstream, and every consumer reads them. If you want 8 steps you change the Loader. Same for the seed, which is why re-running the graph without touching the Loader gives you the same clip back.

Where people get burned

• "Pipe does not contain an audio VAE. Use the PIPE of SAX MiniMax H3 Loader." You fed it a PIPE from the regular SAX Loader. The H3 sampler needs the H3 loader's pipe, which is the only thing that carries an audio VAE.
• "Requires a ComfyUI version providing comfy_extras.nodes_custom_sampler (RandomNoise, KSamplerSelect, ...)." Update ComfyUI to 0.30.0+. The sampler borrows core nodes and says so by name when they're missing, which is more than most packs manage.
• Raising fps to get smoother motion. It won't. H3 generates at 24fps and the Director's own fps output is always 24; higher values just retime the container the frames land in. Leave it unless you know exactly why you're changing it.
• Turbo LoRA, mismatched steps. If you loaded the 4-step or 8-step FL2VA turbo LoRA in the Loader, set steps to 4 or 8 there to match, and expect to nudge the Director's shift_video. Running a turbo LoRA at 20 steps is how you get a mushy clip and blame the sampler.
• Judging H3 on one clip. The first-wave H3 samples posted to r/StableDiffusion split violently - the same model produced lush cinematic output for some and stiff, video-game-looking mush for others, and the thread consensus was that prompt craft and settings (explicit camera directions, the reference-to-video path) dominated the result far more than the model did. Run it a few times before forming an opinion.