I know that Google Chrome has an autoplay policy where videos with audio cannot be autoplayed. How come websites like YouTube and Twich are able to bypass this? How can they autoplay videos with audio?
It looks like they're specially white-listed.
Chrome does this by learning your preferences. If you don’t have browsing history, Chrome allows autoplay for over 1,000 sites where we see that the highest percentage of visitors play media with sound. As you browse the web, that list changes as Chrome learns and enables autoplay on sites where you play media with sound during most of your visits, and disables it on sites where you don’t. This way, Chrome gives you a personalized, predictable browsing experience.
source: https://blog.google/products/chrome/improving-autoplay-chrome/