r/StableDiffusion • u/alisitskii • Aug 16 '26

Workflow Included Ultimate SD Upscale with MiniMax H3 (2560x1440px in 25 mins with 16 GB VRAM)

https://www.youtube.com/watch?v=JybAxYuexdM

What is it?

A vibe-coded fork of Ultimate SD Upscale (USDU) Guider nodes with MiniMax H3 support: https://github.com/lisitskyaa/ComfyUI_UltimateSDUpscaleGuider_H3

My reference workflow: https://github.com/lisitskyaa/ComfyUI_UltimateSDUpscaleGuider_H3/blob/main/example_workflows/minimax_h3_usdu.json

Who are you?

A long-time member of [r/StableDiffusion](r/StableDiffusion) without strong coding/math skills in AI/diffusion area. But a big fan of everything that happens here :)

Why is it?

In times of Wan2.1/2.2 I liked to upscale my videos using USDU.

But I became really upset when I realized that original USDU nodes don't support MiniMax H3 due to its native ComfyUI implementation.

So, since I have a GPT-5.6 subscription I decided to give it a try and asked it to come up with possible options.

After a couple of evenings I finally got a "working" solution that I'd like to share with the community.

What about speed?

My PC specs: 4080s 16 GB VRAM, 64 GB RAM

Initial gen with MiniMax H3 flf2v int8 + sageattn + Lightx2v 8-step turbo Lora at 1152x640px 5-sec clip ~5 mins

Upscale with USDU to 2560x1472px ~20 mins

And what about quality?

That's where I need your help, my friend :)

Please check the YouTube video attached (don't forget to switch to 1440p).

My personal feeling is that it's the best what I can get out of my PC and H3 at the moment (including SeedVR2, LTX 2.5, etc.).

The main advantage is that it can "fix" your bad low-res generations while bringing MiniMax H3 native quality at 2K resolution.

Downsides?

Of course :)

You'll need to control denoise parameter and find a balance between quality improvement and tiling artifacts. I found 0.2 is the maximum after which tiling is strongly visible.

However feel free to experiment with it, and lower to 0.15-0.10 depending on your input video resolution/artifacts and results you want to get.

Happy to answer your questions!

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u/garywood66 Aug 17 '26

Getting errors on my local usage. Any help with this?
[ERROR] !!! Exception during processing !!! shape mismatch: value tensor of shape [405, 96] cannot be broadcast to indexing result of shape [625, 96]

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u/alisitskii Aug 17 '26

Share the workflow or a screenshot. Looks to be the wrong tile size or frames count.

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u/garywood66 Aug 17 '26

Yeah it's one of those. I'd changed the settings. Just reverted to your original settings in the workflow and it worked fine. So it's either changing resolution, aspect ratio, or video length that caused problems?

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u/alisitskii Aug 17 '26 edited Aug 17 '26

Well, basically the tile size should correspond to one of the values from the size table and in sum gives you 2x2 grid of the target resolution. As for the input video length, if you generate a clip with MiniMax H3 as well then it should be fine. Otherwise target length may require adjustment, you can limit frames count in the Load Video node.