From the Safari Menu Bar click Safari/Empty cache. Relaunch Safari. See if that makes a difference. If not...
Try opening Safari in 32-bit mode, not 64. Right or control click the Safari icon in the Applications folder, then click: Get Info In the Get Info window click the black disclosure triangle next to General so it faces down. Select 32 bit mode. Also, (in that same window) make sure Safari is NOT running in Rosetta. Relaunch Safari.
If you still have problems, go to the Safari Menu Bar, click Safari/Preferences. Make note of all the preferences under each tab. Quit Safari. Now go to ~/Library/Preferences and move this file
com.apple.safari.plist to the Desktop.
Relaunch Safari. If you can view video content, then move that .plist file to the Trash.
You could also try logging into another user account, launch Safari there and see if the same thing happens. If it does, then it's a system wide glitch, not just your home folder.
The Vimeo help forum may offer some insight.
http://vimeo.com/help/forum
🙂