Author here: for some sites, that approach works well, and this is what I originally did (and why I decided to write streamsh in bash). Have a look in the "tricks" directory and you'll see some of the much simpler solutions that are tried first. However, an increasing number of sites try to hide the URL, and through increasingly complicated means. The article is about vidbull.com, but there are others. They often also layer multiple obfuscators (vidbull uses both JS obfuscation and URL encryption for example). While it's true you can get pretty far just by scanning for mp4s on some mirrors, they are becoming fewer and farther between.