Yes as the other's said you must change it in your settings, it is linked to the cookies too.
But it is possible. For sure because sometimes it didn't autoplay at my computer, but I didn't pay attention how or why...
It also depends on the device you're watching it with. Just turn teh slider off, so that it's not blue anymore. You can do the same on your tablet or laptop.
picture with autoplay sign
I guess they added this possibilty, because it wasn't always like that...
Anyways that's a possibilty, teh easiest one.