Video quality with DSLR is really grainy, why?

I'm shooting with a d90 with a nikon 20mm 2.8 in 720p mode. The quality is really bad though… Does anyone know why this is going on?

Yes it is completely cause by low light, you will need to change the iso setting and open up the aperture, this will allow light and should depending on how low the light is normal non grainy video

It is all due to the low light conditions.

Flip UltraHD Video Camera - 2 Hours (3rd Generation) NEWEST MODEL is a powerful, easy-to-use, fairly cheap video camera; it records @ 1280 x 720, 60 FPS, and can hold about two full hours of video at that capacity. It fits neatly in a shirt pocket and is pretty much ideal for recording anything that doesn't need to be professionally produced film, from home movies to recording interviews. It comes packaged with a basic editing program that's designed to make it as easy as possible to produce basic home movies and post them to the web.

There's nothing wrong with the recording. Now, the subject matter is a different matter.

Do you get paid for the number of hits?