If you try to embed a YouTube video into an article, and it doesn't appear, it might be because you're using the shortened YouTube URL. Try replacing the shortened YouTube URL embed (e.g., youtu.be/123456) with the longer “embed” code snippet from YouTube's "Share" button under the video. Insert that code snippet into the article using Base's "code view". (The last button on the right of the toolbar in the Base article admin.)