IOS – How to fix Youtube videos only displaying black with sound in iOS’s Safari

There should be a preference thing on YouTube to select HTML5, but they've reorganized the page so many times since I last tracked it down that I have no idea where it is now.

Instead, I have ClickToFlash installed (it's under "Most Popular" in the Safari Extensions Gallery); open its preferences (Safari Preferences... > Extensions) and you can tell it to always use HTML5 for YouTube and other sites that support HTML5 in place of Flash.

This sounds like a problem with the Flash player. you can edit the flash player's settings by going to: http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html

In the section "Website Storage Settings", increasing the amount of data youtube.com can store on your computer might help. Completely deleting youtube.com from the list of visited websites might also help (since that might get rid of any corrupt data).

If that doesn't work you can also try deleting the flash player's cache files manually.

just delete all the folders out of:

/Users/[YOUR USER NAME]/Library/Caches/Adobe/Flash Player/AssetCache

The folders should have names that look similar to "5PXNHG84" or "KK4Y5DSK".

Unfortunately, Flash for OS X (and linux) has never seemed to work as well as it does on windows. So what I just described still may not solve your problem, but it's worth a shot.