ComfyUI-LTX-GapFill

ComfyUI-LTX-GapFill

This node is designed for Safe For Work (SFW) workflows only. It uses Google Gemini 2.5 Flash, which enforces Google's content policies. Do not use this node with NSFW imagery or prompts — requests containing inappropriate content will be rejected by the Gemini API.

A ComfyUI custom node that brings the "Fill with Video" AI prompt suggestion feature from LTX Desktop into ComfyUI workflows.

All credit for the original feature, system prompt design, pipeline architecture, and AI integration goes to the Lightricks team. This node is a faithful port of their work — the system prompt, Gemini payload structure, and frame analysis approach are reproduced verbatim from the LTX Desktop source code. Please support their work:

• LTX Desktop: https://github.com/Lightricks/LTX-Desktop
• LTX-Video models: https://github.com/Lightricks/LTX-Video
• Lightricks: https://www.lightricks.com

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What It Does

This node uses Google Gemini 2.5 Flash to analyze frames and prompts from two neighboring video clips, then returns a suggested text prompt describing what should go between them. That prompt is wired into any LTX sampler node to generate the bridging video.

Use Cases

Gap filling The primary use case — you have two clips on a timeline with empty space between them. Provide the last frame of clip A and the first frame of clip B, and Gemini suggests a prompt for a new clip that flows naturally between both shots.

Transitions Feed any two frames from different scenes, shots, or styles to get a prompt for a transition clip that matches the visual tone of both sides and bridges them smoothly.

First frame / last frame situations Only have one side? The node works one-sided too:

• Supply only clip_before_last_frame to generate something that naturally leads out of a clip
• Supply only clip_after_first_frame to generate something that naturally leads into a clip
• Useful for generating an opening shot, a closing shot, or extending a clip at either end

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Install

1. Copy this folder into your ComfyUI/custom_nodes/ directory
2. Install dependencies:

   pip install requests Pillow numpy
   

   (all three are almost certainly already present in a standard ComfyUI environment)
3. Restart ComfyUI

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Node: LTX-GapFill Prompt (LTX Video Bridge)

Found under LTX → Gap Fill in the node browser.

Inputs

Input	Type	Required	Description
seed	INT	Yes	ComfyUI cache-buster only — not sent to Gemini. Change to force re-run when all other inputs are unchanged.
gemini_api_key	STRING	Yes	Free key from https://aistudio.google.com/app/apikey
model	DROPDOWN	Yes	Gemini model to use (all free tier with limitations)
custom_model	STRING	No	Override model dropdown with any Gemini model ID — leave blank to use dropdown
prompt_style	DROPDOWN	Yes	Controls length and focus of the generated prompt (see Prompt Styles below)
gap_duration	FLOAT	Yes	Duration of the gap or desired clip length in seconds
resize_before_send	BOOLEAN	Yes	Resize images before sending (default: True, recommended)
max_size_px	INT	Yes	Longest edge in pixels when resizing (default: 512)
clip_before_last_frame	IMAGE	Optional	Connect the clip before the gap — last frame auto-selected
clip_after_first_frame	IMAGE	Optional	Connect the clip after the gap — first frame auto-selected
prompt_before	STRING	Optional	Prompt or description of the clip before the gap
prompt_after	STRING	Optional	Prompt or description of the clip after the gap
custom_system_prompt	STRING	Optional	WARNING: Overrides prompt_style entirely. A poorly written prompt wastes tokens and counts against your daily quota. Leave