In the video there is no usb cable to power the device like the chromecast or roku stick.
I suppose it needs one too ?
It's a shame that advertisement for these devices "lie" about it.
They prefer having external power because many HDMI ports don't supply enough consistently, but don't require it.
I am not 100% sure what the power requirements for a Chromecast are, I'm 100% sure it is more then 50mA.
If you are plugging in your Chromecast to your TV without the USB and it is working it's because you have a MHL-HDMI that provides up to 900mA of power.