Comfyui-MMH3-UltimateUpscale
Upscale long, high-resolution MiniMax H3 video on a VRAM-limited GPU — in a single node.
This node re-samples (enhances / upscales) an already-denoised MiniMax H3 AV latent through the full auto pipeline under tight VRAM constraints: it processes the clip with temporal chunking (so arbitrarily long videos fit in memory) + spatial tiling (so arbitrarily high resolutions fit in memory), keeping peak VRAM bounded to a single tile, while preserving the audio track intact.
MiniMax H3 generates video as a nested latent that bundles 24-channel video and 32-channel audio in one tensor. Standard ComfyUI upscale nodes do not understand this structure. MMH3 Ultimate Upscale wraps the entire temporal split -> latent upscale -> spatial split -> per-tile sampling -> spatial stitch -> temporal stitch loop into one node, so you can upscale a finished H3 clip the same way you would upscale a normal latent — without breaking audio and without running out of VRAM even on small cards.
Changelog
- 20260905 - Latent upscale checkpoints are now
.safetensors only. Pickle formats (.pth / .pt / .ckpt) are no longer listed or loaded, because torch.load() on a pickle checkpoint can execute arbitrary code and weights_only=True is not a reliable mitigation on torch < 2.6 (CVE-2025-32434). If you were using minimax_h3_latent_upscaler_3d_fp32.pth, convert it once (see Upscale model format) or switch to the fp16 / bf16 .safetensors build. The scanner now also searches every registered latent_upscale_models directory (including extra_model_paths.yaml) instead of only the first one.
- 20260831 - Rearrange the code structure. Bugs fix and add some features. Add
dynamic fade to improve seam removal when denoise step>1. Add brightness match to to help reduce brightness flickering.
- 20260829 - Add new nodes about Fun ControlNet to enhance performance. Two nodes
MMH3 Fun Controlnet Inpaint and MMH3 Spatial Inpaint Params, which help seamless spatial stitching and better consistance in higher denoise condition. To use these nodes you have to merge kijai's pull request in comfyui.
- 20260825 - New experimental
LTX25 Ultimate Upscale node. Built on top of the MMH3 pipeline, it now also supports LTX2.5 nested AV latents (video [B,128,T,H,W] + audio [B,C,time,freq]) in a single node: temporal split -> latent upscale (fixed 2x model upscale, then interpolated to the target width/height) -> spatial split -> per-tile sampling -> stitch. Three optional param nodes are provided: LTX25 Latent Upscale Params, LTX25 Temporal Split Params, and LTX25 Spatial Split Params. Audio is buggy so you should use original audio latent. These nodes are highly experimental, so don't rely on them.
Features
- Upscale long + high-res video on limited VRAM. The core design goal: temporal chunking keeps arbitrarily long clips in memory, spatial tiling keeps arbitrarily high resolutions in memory, and only one tile is sampled at a time — so peak VRAM stays at a single tile regardless of video length or output resolution.
- One node, full pipeline. Temporal chunking (outer loop), optional latent upscale, spatial tiling (inner loop), per-tile diffusion sampling, then spatial + temporal stitching — all driven by a single
MMH3 Ultimate Upscale node.
- Temporal chunking for long videos. A long clip is cut into overlapping time chunks; each chunk is processed independently and stitched back together.
- Two upscale modes per chunk:
- H3 3D model-based upscaler (
MMH3 Latent Upscale with Model Params) — uses the minimax_h3_latent_upscaler_3d_*.safetensors checkpoints from the latent_upscale_models folder.
- Model-free interpolation (
MMH3 Latent Upscale Params) — resizes the video latent spatially (nearest / bilinear / area / bicubic) with no extra model, audio untouched. Mirrors ComfyUI's Upscale Latent but keeps the nested AV structure.
- Spatial tiling for bounded VRAM. Each chunk is split into tiles and only one tile is sampled at a time, so peak VRAM stays at one tile instead of the whole frame.
- Audio preserved. The audio portion of the latent is carried through unchanged on every chunk and stitch — it is never re-sampled.
- Optional stages.
latent_upscale_param, temporal_split_param, and spatial_split_param are all optional. Leave any of them unconnected to skip that stage (no upscale / single chunk / whole-chunk sampling).
- VRAM-friendly model management. The 3D upscaler is offloaded back to CPU after each use, and the diffusion model is unloaded while the upscaler runs, so H3 + upscaler are never resident at the same time (the next sample reloads H3 automatically).
- Per-piece conditioning. Conditioning is re-anchored in time per chunk and spatially cropped per tile; keyframe video latents are resized to the (possibly upscaled) chunk grid.
Advantages
Temporal consistency & smooth time transitions
- Frame-0 anchor. At the start of each chunk (except the first), the chunk's frame-0 keyframe is replaced by the previous chunk's re-sampled boundary frame (
anchor_conditioning, controlled by anchor_strength, default 0.999 — mirroring the Anchor MiniMax H3 Latent node). This removes detail mismatch at the chunk seam.
- Cross-fade stitching. Overlapping chunks are blended with a linear cross-fade (
temporal_append / _crossfade) over the overlap region, so transitions between chunks are smooth rather than hard-cut.
Pixel-space consistency & smooth spatial transitions
- Frozen overlap mask. Each tile is sampled at its true extent, but the overlap strips it shares with already-stitched neighbors are pre-filled from the accumulated result and locked with a
noise_mask (spatial_fade_mask). The re-sample is therefore only allowed to change the free interior; the shared seam content is preserved exactly.
- Masked write-back. After sampling, the frozen seam region is written back with
torch.where(band, stitched, tile), guaranteeing the already-consistent seam is never overwritten.
- Configurable seam blending. The overlap band between tiles is blended with
overlap_blend (linear / smoothstep / overwrite / midpoint) under overlap_mode (earlier wins / later wins), giving full control over how adjacent tiles transition into each other — smooth, not blocky.
Other
- Peak VRAM bounded to a single tile thanks to spatial tiling + model offloading.
- Audio never re-sampled — no audio artifacts, no extra cost.
- No forced model download — pick the model-based 3D upscaler or the model-free interpolation path.
Why chunked re-sampling beats dynamic VRAM offloading
Modern PyTorch/CUDA can shuffle weights between RAM and VRAM on demand, so in principle you can generate without tiling even when the working set exceeds VRAM. In practice this is dramatically slower, and the reason is a bandwidth gap of one to two orders of magnitude:
| Path |
Typical bandwidth |
| GPU VRAM (GDDR/HBM) |
~1000 GB/s |
| PCIe 4.0 x16 (RAM ↔ GPU) |
~32 GB/s |
| PCIe 5.0 x16 |
~64 GB/s |
Diffusion sampling runs tens of sequential denoising steps, and a transformer revisits its blocks in the same cyclic order every step — the worst case for any residency cache. If the weights do not fit, nearly all non-resident bytes are re-moved over PCIe on every step:
T(offload) ≈ steps × non-resident bytes / PCIe_bandwidth ← bandwidth-bound
T(chunked) ≈ pieces × FLOPs_piece / GPU_FLOPS ← compute-bound
Unified-memory page faults additionally serialize the CUDA stream, so GPU utilization collapses to single digits. Chunked re-sampling instead bounds the peak working set to all weights + one piece's activations, keeping every forward pass compute-bound. The price is only a small, predictable redundancy:
- spatial: ≈ ((tile + overlap) / tile)² — e.g. 512 px tile with 128 px overlap → ×1.56
- temporal: ≈ (chunk + overlap) / chunk — e.g. 136 frames with 17 overlap → ×1.13
A constant factor of ~1.2–1.8× always beats a 15–60× per-byte penalty. Host↔VRAM offloading only pays when the excess is small and every moved byte gets high reuse; large-DiT multi-step denoising satisfies neither.
Tuning chunk & tile sizes for your VRAM
Per-piece sampling VRAM ≈ model weights + activations, where the activation part scales roughly with chunk_length × tile_width × tile_height:
- Too large → the piece spills into the streaming regime described above (15–60× slowdown per byte).
- Too small → the fixed overlap taxes dominate: each axis pays
(size + overlap) / size, so e.g. shrinking tiles to 256 px with a fixed 128 px overlap already costs ×2.25 in redundant pixels.
Aim for the largest pieces that keep peak VRAM just under capacity (watch ComfyUI's VRAM meter during the first tile), keeping total redundancy within roughly ×1.3–1.8. Starting points for H3:
| GPU VRAM |
tile_width × tile_height |
chunk_length (multiple of 17 px frames) |
| 8 GB |
320–384 |
34–68 |
| 12 GB |
384–512 |
51–102 |
| 16 GB |
512–576 |
102–153 |
| 24 GB |
576–768 |
136–170 |
Notes:
- Values assume quantized/pruned H3 checkpoints; measure your own peak and adjust one step at a time.
- Keep tiles ≥ 256 px, or the fixed overlaps eat the budget.
- The LTX25 node follows the same principle on its 32-px grid; if your checkpoint cannot stay resident at all, smaller pieces still help by minimizing spill traffic.
Nodes
| Node |
Role |
| MMH3 Ultimate Upscale |
Main node. Runs the whole loop. Inputs: latent, conditioning, model, noise, sampler, sigmas, optional negative + cfg, and the three optional param inputs. |
| MMH3 Temporal Split Params |
chunk_length (px frames, multiple of 17), temporal_overlap (multiple of 17), anchor_strength. |
| MMH3 Spatial Split Params |
tile_width / tile_height (px, multiple of 32), spatial_w_overlap / spatial_h_overlap (px, multiple of 32), fade_width / fade_height (seam mask fade), min_tile_size, overlap_mode, overlap_blend. |
| MMH3 Latent Upscale with Model Params |
H3 3D model upscaler: model_name, width, height (snapped to a multiple of 32), device, precision. |
| MMH3 Latent Upscale Params |
Model-free interpolation: method, width, height (snapped to a multiple of 32). |
Typical workflow
- Generate an H3 AV latent with MiniMax H3 (video + audio in one latent).
- (Optional)
MMH3 Temporal Split Params → connect to temporal_split_param.
- (Optional)
MMH3 Latent Upscale with Model Params or MMH3 Latent Upscale Params → connect to latent_upscale_param.
- (Optional)
MMH3 Spatial Split Params → connect to spatial_split_param.
- Feed
latent, conditioning, model, noise, sampler, sigmas into MMH3 Ultimate Upscale.
- Decode the output latent with the H3 VAE.
The width/height you set for upscaling must match the conditioning's generation size (the size the video was conditioned at, after upscale).
MMH3 Latent Upscale with Model Params only lists and loads .safetensors checkpoints (.sft is accepted as well, matching ComfyUI core). Pickle formats (.pth / .pt / .ckpt) are skipped while scanning and are rejected before the file is opened.
Why: torch.load() on a pickle checkpoint can execute arbitrary code the moment the model is selected. weights_only=True reduces the risk but is not a reliable mitigation on torch < 2.6 (pickle-time bypass, CVE-2025-32434). Refusing pickle entirely removes that surface.
If you have a .pth checkpoint you trust (for example minimax_h3_latent_upscaler_3d_fp32.pth), convert it once:
import torch, safetensors.torch
sd = torch.load('model.pth', map_location='cpu', weights_only=True)
sd = sd['model'] if isinstance(sd, dict) and 'model' in sd else sd
safetensors.torch.save_file(sd, 'model.safetensors')
If weights_only=True fails, the file is not a plain state dict and should not be trusted — don't work around it by switching back to weights_only=False. Checkpoints left in the folder are reported as ignored in the console at startup.
Reference Projects
This node is built on top of following existing community projects:
The H3 3D upscaler network code and normalization statistics are adapted from the second project; the temporal/spatial split, anchor and append logic follow the first.
This project was vibe-coded by AI, If you run into any problems, it's best to search with AI.😂
A ComfyUI custom node that upscales long, high-resolution MiniMax H3 AV video latents on VRAM-limited GPUs, using temporal chunking and spatial tiling inside a single node while keeping the audio track intact.