How scroll-recording extensions work
An extension uses Chrome’s tab capture to record the page you are looking at while a script scrolls it. Scroll Capture, one of the longest-running, describes itself as a tool for designers and developers making portfolio captures: its scroll eases in and out, can calculate the duration from the scroll distance, and it can also script mouse events, text input, custom CSS and zoom. Its listing shows about 30,000 users. Newer ones, such as ScrollCinema, offer free tiers with paid upgrades for styles and viewport options.
Because the capture happens in your tab, an extension sees exactly what you see, including pages you are signed in to. That is their real advantage over any URL-based tool.

