The web is littered with videos that play automatically that nobody asked for
It's not your imagination. There are videos playing on most of those websites you visit, whether you wanted them to play or not. But that dynamic may soon change if new web browsers coming from Apple and Safari gain wide adoption. These browsers will have some ad blocking products baked in – including features designed to block some autoplay videos.
You can block videos from playing automatically in Google Chrome by installing a free Disable HTML5 Autoplay extension found in the Chrome Webstore.