I know, but it's also my primary viewing pace. Our TV doesn't even do 720p
Turns out this is correct. It won't power the external drive. I'm guessing the adapter doesn't pass enough power, because I'm sure the Thunderbolt port does have enough on tap.
Unfortunately my encosure doesn't have an auxiliry power socket, so I can't even test it with an external power supply. I think I have a 90MB/s SD card though - I'll try that tonight.