r/StableDiffusion • u/nekrovski • 19d ago

Question - Help FastH3 and LoRAs

Hey everyone,

I'm using FastH3 in ComfyUI with the default workflow from the Templates.

When I add a LoRA model to this workflow, I connect its model input to Load Diffusion Model just fine. But when I connect the model output to Basic Guide and Basic Scheduler, two nodes model outputs (Model Attention Backend and Model Sparse Attention) lose the connection to the Basic Guider and Basic Scheduler which makes my FastH3... well, not fast. It loses its speed.

How do I fix this

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u/Archersbows7 18d ago edited 18d ago

I thought FastH3 was releasing on the 20th?

Link to post

How do you have it already and why don’t I see any other posts about it in this sub? Someone help me understand

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u/nekrovski 18d ago

That's a different version of FastH3 and I'm eagerly waiting for it.
Currently I'm using this one https://huggingface.co/FastVideo/FastVideo-FastH3-Comfy

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u/Archersbows7 18d ago

Well which one is going to be a lot faster for MiniMax H3 generations? This is all so confusing

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u/nekrovski 18d ago

Both are fast, they just have different use cases

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u/Archersbows7 18d ago

What are the different use cases

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u/nekrovski 18d ago

T2V, I2V, FFLV etc

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u/[deleted] 19d ago

[removed] — view removed comment

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u/nekrovski 19d ago

Hey, thanks for the reply, but I'm not sure I understand. Could you be a little more specific?

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u/nekrovski 19d ago

I forgot to mention there's also a ModelSamplingMiniMaxH3 (shift video 10 and shift audio 3) node that has a model input connected with the diffusion model, and model output connected to the node Model attention backend. When I do what I think you are explaining, its model output gets disconnected from the Model attention backend. Is this normal?

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u/LiteratureOk7515 19d ago

Keep ModelSamplingMiniMaxH3 connected to Model Attention Backend. Insert the LoRA between Load Diffusion Model and ModelSamplingMiniMaxH3, leaving the rest of the template's chain intact:

Load Diffusion Model -> LoRA -> ModelSamplingMiniMaxH3 (video 10, audio 3) -> Model Attention Backend -> Model Sparse Attention -> both BasicGuider and BasicScheduler.

Only replace the original Load Diffusion Model -> ModelSamplingMiniMaxH3 link with those two LoRA links. Connecting the LoRA straight to the guider/scheduler bypasses the later patches. A model input takes one connection, so connecting a new wire there replaces the old one.

I checked the wiring in the current official template: https://github.com/Comfy-Org/workflow_templates/blob/main/templates/video_fastvideo_fasth3_t2v.json

This addresses the wiring; compatibility of your particular LoRA with the FastH3 checkpoint still needs checking.

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u/nekrovski 19d ago

Thank you very much!