Fortunately, support the adapter (or the MacBook Air) the sound transmission, thus I can with my Mac also wired on my TV not only watch movies, but also hear the sound through the TV. So it should be, but just do not seem to be working with all adapters.
A little tip: the sound is not transmitted automatically to the screen connected via HDMI, this must be uniquely configured in System Settings so.
Kindly, the MacBook Air (Late 2011) also supports all frame rates (24/50/60 Hz), so every movie can be enjoyed absolutely smoothly.
I am completely satisfied with this lowcost adapter!