The project

About LM Subs

Google NotebookLM turns dense papers, lecture slides, and technical documentation into spoken Video Overviews, but the built-in player ships without closed captions, chapter navigation, or downloadable subtitle files. For anyone reviewing a lecture in a library, searching for one specific formula, or following technical vocabulary in a second language, missing captions turn a strong study tool into a black box.

Who builds it

LM Subs is built by Sarang (@sarang-cmd), a computer science student and agentic engineer based in Germany. The project is open source under the MIT license and is not affiliated with Google LLC.

Design decisions worth knowing

• Audio is extracted in the browser, so roughly 3 MB of audio is sent instead of a 50 MB video.
• You bring your own key, and the recommended providers have permanent free tiers.
• Caption controls dock inside NotebookLM's own play bar instead of floating above it.
• Cloud sync is opt-in per category, and every page says when numbers are sample data.