ComfyUI SeC Nodes

ComfyUI custom nodes for SeC (Segment Concept) - State-of-the-art video object segmentation that outperforms SAM 2.1, utilizing the SeC-4B model developed by OpenIXCLab.

Changelog

v1.2 (2025-10-16) - FP8 Removal & Performance Optimizations

⚠️ IMPORTANT BREAKING CHANGE: FP8 support has been removed due to fundamental numerical instability issues. Use FP16 or BF16 models instead.

What Changed:

• FP8 quantization disabled - produces NaN values in language model embeddings during scene detection
• All users should migrate to FP16 or BF16 models (same segmentation quality, fully reliable)
• Memory optimization: Pre-allocated output tensor (saves 600-800MB VRAM spike)
• Scene detection resolution optimization: 1024x1024 → 512x512 (saves 200-400MB, no quality impact)

Full Technical Details: See CHANGELOG.md for comprehensive investigation and FP8 failure analysis.

v1.1 (2025-10-13) - Single-File Models

• Single-file model formats: Download just one file instead of sharded 4-file format

Download: Single-file models available at https://huggingface.co/VeryAladeen/Sec-4B

What is SeC?

SeC (Segment Concept) is a breakthrough in video object segmentation that shifts from simple feature matching to high-level conceptual understanding. Unlike SAM 2.1 which relies primarily on visual similarity, SeC uses a Large Vision-Language Model (LVLM) to understand what an object is conceptually, enabling robust tracking through:

• Semantic Understanding: Recognizes objects by concept, not just appearance
• Scene Complexity Adaptation: Automatically balances semantic reasoning vs feature matching
• Superior Robustness: Handles occlusions, appearance changes, and complex scenes better than SAM 2.1
• SOTA Performance: +11.8 points over SAM 2.1 on SeCVOS benchmark

How SeC Works

1. Visual Grounding: You provide initial prompts (points/bbox/mask) on one frame
2. Concept Extraction: SeC's LVLM analyzes the object to build a semantic understanding
3. Smart Tracking: Dynamically uses both semantic reasoning and visual features
4. Keyframe Bank: Maintains diverse views of the object for robust concept understanding

The result? SeC tracks objects more reliably through challenging scenarios like rapid appearance changes, occlusions, and complex multi-object scenes.

Demo

https://github.com/user-attachments/assets/5cc6677e-4a9d-4e55-801d-b92305a37725

Example: SeC tracking an object through scene changes and dynamic movement

https://github.com/user-attachments/assets/9e99d55c-ba8e-4041-985e-b95cbd6dd066

Example: SAM fails to track correct dog for some scenes

Features

• SeC Model Loader: Load SeC models with simple settings
• SeC Video Segmentation: SOTA video segmentation with visual prompts
• Coordinate Plotter: Visualize coordinate points before segmentation
• Self-Contained: All inference code bundled - no external repos needed
• Bidirectional Tracking: Track from any frame in any direction

Installation

Option 1: ComfyUI-Manager (Recommended - Easiest)

1. Install ComfyUI-Manager (if you don't have it already):

   • Get it from: https://github.com/ltdrdata/ComfyUI-Manager

2. Download a model (see Model Download section below)

3. Install SeC Nodes:

   • Open ComfyUI Manager in ComfyUI
   • Search for "SeC" or "SecNodes"
   • Click Install
   • Click Restart when prompted

4. Done! The SeC nodes will appear in the "SeC" category

Option 2: Manual Installation

Step 1: Install Custom Node

cd ComfyUI/custom_nodes
git clone https://github.com/9nate-drake/Comfyui-SecNodes

Step 2: Install Dependencies

ComfyUI Portable (Windows):

cd ComfyUI/custom_nodes/Comfyui-SecNodes
../../python_embeded/python.exe -m pip install -r requirements.txt

Standard Python Installation (Linux/Mac):

cd ComfyUI/custom_nodes/Comfyui-SecNodes
pip install -r requirements.txt

Step 3: Restart ComfyUI

The nodes will appear in the "SeC" category.

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Model Download

Download ONE of the following model formats:

The SeC Model Loader will automatically detect and let you select which model to use. Download from https://huggingface.co/VeryAladeen/Sec-4B and place in your ComfyUI/models/sams/ folder:

• SeC-4B-fp16.safetensors (Recommended) - 7.35 GB
  • Best balance of quality and size
  • Works on all CUDA GPUs
  • Recommended for all systems
• SeC-4B-bf16.safetensors (Alternative) - 7.35 GB
  • Alternative to FP16, better for some GPUs
• SeC-4B-fp32.safetensors (Full Precision) - 14.14 GB
  • Maximum precision, highest VRAM usage
  • Better compatibility on some older GPUs

⚠️ FP8 Support Removed (v1.2)

• FP8 quantization has been removed due to numerical instability issues
• All users should use FP16 or BF16 models instead (same quality, fully reliable)
• See CHANGELOG.md for full technical investigation

Alternative: Original Sharded Model

For users who prefer the original OpenIXCLab format:

cd ComfyUI/models/sams

# Download using huggingface-cli (recommended)
huggingface-cli download OpenIXCLab/SeC-4B --local-dir SeC-4B

# Or using git lfs
git lfs clone https://huggingface.co/OpenIXCLab/SeC-4B

Details:

• Size: ~14.14 GB (sharded into 4 files)
• Precision: FP32
• Includes all config files in the download

Requirements

• Python: 3.10-3.12 (3.12 recommended)
  • Python 3.13: Not recommended - experimental support with known dependency installation issues
• PyTorch: 2.6.0+ (included with ComfyUI)
• CUDA: 11.8+ for GPU acceleration
• CUDA GPU: Recommended (CPU supported but significantly slower)
• VRAM: See GPU VRAM recommendations below
  • Can reduce significantly by enabling offload_video_to_cpu (~3% speed penalty)

Note on CPU Mode:

• CPU inference automatically uses float32 precision (bfloat16/float16 not supported on CPU)
• Expect significantly slower performance compared to GPU (~10-20x slower depending on hardware)
• Not recommended for production use, mainly for testing or systems without GPUs

Flash Attention 2 (Optional):

• Provides ~2x speedup but requires specific hardware
• GPU Requirements: Ampere/Ada/Hopper architecture only (RTX 30/40 series, A100, H100)
  • Does NOT work on RTX 20 series (Turing) or older GPUs
• CUDA: 12.0+ required
• Windows + Python 3.12: Use pre-compiled wheels or disable flash attention
• The node automatically falls back to standard attention if Flash Attention is unavailable

GPU VRAM Requirements

Minimum: 10GB VRAM

• Use FP16 or BF16 model
• Enable offload_video_to_cpu: True if you experience VRAM issues
• Resolution and frame count have minimal VRAM impact when video offloading is enabled
• VRAM usage remains consistent (~8.7GB) regardless of video resolution or duration

Recommended: 16GB+ VRAM

• Run without offloading for best performance
• More comfortable for extended workflows and multiple sequential runs

VRAM Management:

• offload_video_to_cpu: Primary VRAM control - saves ~2-3GB with only ~3% performance impact
• mllm_memory_size: Lower values (5-10) for additional VRAM savings if needed (affects semantic quality slightly)
• use_flash_attn: Enables faster inference (requires RTX 30/40 series or newer)

Pro Tips:

• Onboard/integrated graphics for display output saves additional VRAM on dedicated GPU
• FP16 is the standard recommendation - best compatibility and reliability
• GPU supports automatic precision detection and optimization

Nodes Reference

1. SeC Model Loader

Load and configure the SeC model for inference. Automatically detects available models in ComfyUI/models/sams/.

Outputs: model

Notes:

• Model Selection: Dynamically shows available models in ComfyUI/models/sams/ directory
  • Download at least one model format (see Model Download section above)
  • Models are loaded in their native precision (preserves memory benefits of model format)
  • FP16 and BF16 have identical sizes (7.35GB) - choose based on GPU preference
• Config files: Bundled in this repo - no separate download needed for single-file models
• Device options dynamically adapt to your system:
  • 1 GPU system: Shows auto, cpu, gpu0
  • 2 GPU system: Shows auto, cpu, gpu0, gpu1
  • 3+ GPU system: Shows all available GPUs
  • No GPU: Shows only auto and cpu
• CPU mode: Automatically converts model to float32 precision (CPU limitation). CPU inference is significantly slower than GPU (~10-20x).
• Flash Attention: Automatically disabled for FP32 models (requires FP16/BF16). Standard attention will be used instead.

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2. SeC Video Segmentation

Segment and track objects across video frames.

Outputs: masks (MASK), object_ids (INT)

Important Notes:

• Provide at least one visual prompt (points, bbox, or mask)
• Output always matches input frame count: If you input 100 frames, you get 100 masks
• Frames before/after the tracked range will have empty (blank) masks
  • Example: 100 frames, annotation_frame_idx=50, direction=forward → frames 0-49 are blank, 50-99 are tracked
  • Example: 100 frames, annotation_frame_idx=50, direction=backward → frames 0-50 are tracked, 51-99 are blank
  • Example: 100 frames, annotation_frame_idx=50, direction=bidirectional → all frames 0-99 are tracked

Input Combination Behavior:

You can combine different input types for powerful segmentation control:

Example Use Cases:

• Bbox + point refinement: Draw bbox around a person, add point on their shirt to segment just the shirt instead of the whole person
• Rough mask + precise points: Draw a rough mask around a person, then add positive points on their face to focus the segmentation
• Mask + negative exclusions: Mask an object, add negative points on unwanted parts (e.g., exclude a hand from a person mask)
• Point filtering: Positive points outside the mask boundary are automatically ignored, preventing accidental selections

⚠ Important Note on Negative Points with Masks:

• Negative points work best when placed inside or near the masked region
• Negative points far outside the mask (>50 pixels away) may cause unexpected results or empty segmentation
• You'll receive a warning in the console if negative points are too far from the mask

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3. Coordinate Plotter

Visualize coordinate points on images for debugging.

Outputs: image (IMAGE)

Tracking Directions

Understanding mllm_memory_size

The mllm_memory_size parameter controls how many historical keyframes SeC's Large Vision-Language Model uses for semantic understanding:

• What it does: Stores frame references (first frame + last N-1 frames) for the LVLM to analyze when scene changes occur
• VRAM impact: Minimal - testing shows values 3-20 use similar VRAM (~8.7GB with offload_video_to_cpu, ~11-13GB without)
• Compute impact: Higher values mean more frames processed through the vision encoder on scene changes
• Quality trade-off: More keyframes = better object concept understanding in complex scenes, but diminishing returns after ~10-12 frames
• Original research: SeC paper used 7 and achieved SOTA performance (+11.8 over SAM 2.1), emphasizing "quality over quantity" of keyframes

Recommended Values:

• Default (12): Balanced approach - good quality for most videos
• Low (5-7): Faster inference, matches original research, ~1-2% VRAM savings
• High (15-20): Maximum semantic context for complex multi-object scenes (no significant VRAM penalty)

Why minimal VRAM impact? The parameter stores lightweight frame indices and mask arrays, not full frame tensors. When scene changes occur, frames are loaded from disk on-demand for LVLM processing. The underlying SAM2 architecture supports up to 22 frames.

Attribution

This node implements the SeC-4B model developed by OpenIXCLab.

• Model Repository: OpenIXCLab/SeC-4B
• Paper: arXiv:2507.15852
• Official Implementation: github.com/OpenIXCLab/SeC
• License: Apache 2.0

Dataset: The original work includes the SeCVOS Benchmark dataset.

Known Limitations

Mask-Only Inputs: Using only a mask or bounding box may result in less stable tracking. This is due to how the underlying SAM2 and MLLM components process mask and bbox inputs. For best results, combine masks/bboxes with coordinate points for more precise control.

Troubleshooting

CUDA out of memory:

• First: Enable offload_video_to_cpu: True (saves ~2-3GB VRAM, only ~3% slower)
• Second: Lower mllm_memory_size to 5-10 (reduces computation at scene changes)
• Third: Process fewer frames at once (split video into smaller batches)
• Use FP16 or BF16 models (confirmed working minimum is 10GB VRAM)

Slow inference:

• Enable use_flash_attn in model loader (requires Flash Attention 2)
• Disable offload_video_to_cpu if you have sufficient VRAM

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Self-contained ComfyUI nodes - just install and segment! 🎉