Video isn’t playing on websites on Safari

There's two things you can do to fix this. First, the simplest way is to just navigate to the website you want to watch videos on, such as youtube. After the website has loaded, move your cursor to the address and search bar, and right click on the website address. If you don't have a right click on your mouse, you and also left click while holding down the Control key on your keyboard.

When you do this, a little context menu will appear, and choose where it says: Settings For This Website

Another small window will pop-up, and it has a bunch of options in it you can change. You're looking for the one that says Auto-Play. To the right of it, you can select three options: Allow All, Stop Media with Sound, and Never Allow.

You're default setting is probably set to Never Auto-Play. You can adjust the setting for each website individually by repeating these steps for any website you want to play videos automatically.

Or if you just want to play all videos everywhere everytime, you can go into your Safari Preferences > Websites > Auto-Play.

There will be a list of every webpage you've visited along with its default setting. Beneath it you can change the default that occurs when you visit a new page. Again set it to whatever you're comfortable with. I like to have them turned off by default and then just hand-pick the few websites i might want to see videos on.

Hope that solves it.