ffmpeg-concat is a Node.js CLI tool and library for concatenating video files with OpenGL-based transitions. It extracts frames from input videos using ffmpeg, applies GLSL transitions between consecutive frames using headless-gl, and transcodes the result to MP4. The architecture is modular with separate modules for frame extraction, transition rendering, audio handling, and final encoding. Key entry points are lib/index.js (library API) and lib/cli.js (command-line interface). The system relies on ffmpeg as a system dependency and wraps it with fluent-ffmpeg for Node.js integration. The code demonstrates solid engineering practices with clear separation of concerns, proper error handling, and test coverage. However, the dependency ecosystem shows signs of age - many packages date to 2018-2019, and the Travis CI configuration uses outdated Node.js versions. The OpenGL-based transition system is the core innovation, allowing complex visual transitions that would be difficult to implement with ffmpeg filter graphs alone. This is a practical tool for video editors and developers needing programmatic video concatenation with visual effects. It's not a research project or data pipeline - it's a production-ready library with CLI support.