why can't I get sound on my youtube videos?

1. System Preferences > Flash Player > Advanced > Delete All

Press the "Delete All" button under “Browsing Data and Settings”.

Install Adobe Flash Player.

http://get.adobe.com/flashplayer/

Download it first.

The next step is important.

Click Safari in the menubar and select “Quit Safari”.

Follow the prompts and install it.

Restart computer. Relaunch Safari.

2. Allow Plug-ins

Safari > Preferences > Security

Internet Plug-ins > "Allow plug-ins"

Enable it.

3. Safari > Preferences > Privacy > Cookies and website data:

Press the “ Remove All Website Data” button.

Press the “Details” button.

Remove YouTube related cookies.

4. Safari > Preferences > Extensions

Turn all extensions off, relaunch Safari and test.

Turn those on one by one and test.