I haven't been able to watch my TVs in Second Life on my Macs (one Mavericks and one Lion) for about a year now. I've wasted countless hours trying to fix the problem, thinking the problem had to do with Adobe. Below is what someone posted over on the Phoenix viewer forum in December 2013. It is sad. Apple or Linden are clearly not interested in fixing this. My enjoyment of SL has gone down considerably. It's a bummer. If you are a Mac user, don't buy an SL TV, you won't be able to use it.
"The broken flash media on Mac where you can hear the sound but not see the video is a known bug and is filed at FIRE-11057
This bug also exists on the official LL viewer.
It will require an update to webkit to fix, which is non-trivial."
And this from another forum.
"Adobe FlashPlayer 11.8.x & Mac OS X: media streaming broken, black or blank video screen, only sound plays ok [ affects all Apple users with OS X 10.6.8 up to 10.9.2 ] - old legacy code in Webkit needs update to CoreGraphics & CocoaEvents"