Two recent changes in the Internet world have conspired to create a problem for Mac users attempting to play YouTube videos. The problem: You attempt to play a YouTube video but all you get is a black, inert rectangle. It's dead. Nothing happens.
Rather than pull your hair out, reinstall everything or think your Mac is broken, here is what's going on:
I) Adobe just recently caught up with the real world, nearly 6 (SIX) years LATE, and started providing a 64-bit version of their Shockwave Player. Gee thanks Adobe. About time, don't you think?
The problem is that you must have Safari running in the same mode as the version of Shockwave Player you have installed. Therefore:
A) If you install the 32-bit version of the Shockwave Player plug-in, you must run Safari in 32-bit mode. You can do this in Safari's Get Info box.II) The other half of the problem is that Google forgot to tell anyone that they are now offering videos on YouTube in .SWF format. This is the Shockwave format, NOT the Flash format .FLV. Therefore the videos play using the Shockwave Player plug-in, NOT the Flash Player plug-in.
B) If you install the 64-bit version of the Shockwave Player plug-in, you must run Safari in 64-bit mode. Be sure to check if this is the case in Safari's Get Info box by verifying that you are NOT running Safari in 32-bit mode.
Once you match up your bit versions of Safari and Shockwave Player, you'll find your YouTube functionality is fine. Adobe warn about this incompatibility problem in one direction, but not the other. Google don't warn you at all. (No wonder both companies have legions of anti-fans).
Also keep in mind that Adobe is in the midst of a flood of security flaws being discovered in their software. This problem is particularly critical with the Shockwave Player, Flash Player, Adobe Reader and Adobe Acrobat because the file formats they play are universal on the Internet. This means that it is CRITICAL to keep up with the entirely IRREGULAR releases of security updates from Adobe. Totally ignore Adobe's idiotic quarterly 'In-Band' schedule for releasing updates. Scheduling security updates is for fools. (I'm talking to you too Microsoft!)
Here is where to keep track of Adobe's latest security holes and updates:
Adobe Security Bulletins and Advisories
Adobe Product Security Incident Response Team (PSIRT) Blog
You can pick which version of Shockwave Player you would like to download and install (32 or 64-bit) HERE.
I regularly rake Adobe over the coals at my Mac-Security blog.
You can read about 32-bit mode versus 64-bit mode at Wikipedia.org.