This covers how to load YouTube transcripts into LangChain documents.

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Setup

You’ll need to install the youtubei.js to extract metadata:
npm
npm install @langchain/community @langchain/core youtubei.js

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Usage

You need to specify a link to the video in the url. You can also specify language in ISO 639-1 and addVideoInfo flag. 
import { YoutubeLoader } from "@langchain/community/document_loaders/web/youtube";

const loader = YoutubeLoader.createFromUrl("https://youtu.be/bZQun8Y4L2A", {
  language: "en",
  addVideoInfo: true,
});

const docs = await loader.load();

console.log(docs);