Ok so i'm familar with the image quality settings, apature, shutter speed, and iso.
Ive been doing test shots and i'm having issues getting crisp, defined video.
on the camera, the videos are smooth and noiseless. However, once on my mac to edit, the low light shots have noise, and the outside shots are very blurred not very sharp.
The camera LCD is small, so it's hard to see noise and focus problem. It's a problem for both still and video. Use low ISO and avoid underexposure to keep the noise in check. Blurry video most of the time has to do with focus problem.
There will be no difference in image quality from iMovie to Final Cut Pro. The difference is only in the features available to you as you edit the movie.
Keep in mind that the T3i does not continuously auto-focus during video. You can either manually focus the camera OR you can use the asterisk (*) key on the back of the camera to ask the camera to re-focus the video (but you may see focus-hunt in your resulting movie unless you cleverly cut the focus-hunt when you're editing on the computer.)
Noise is simply a result of excessive ISO in very low light situations. Use of a "faster" lens (a lens which has a wider aperture is sometimes called a "fast" lens because collecting more light means it can use shorter exposure times.) and this would allow you to reduce the ISO setting (possibly substantially). For example if you could reduce to f/2... that would allow the camera to collect 8 times more light than at f/5.6. That would allow you to cut the ISO by 3 stops (e.g. if you were using... say ISO 6400, it would allow you to drop to ISO 800 -- saving you quite a bit of noise.) But the trade off is that the depth of field (the range of distances nearer and farther from the intended focus distance at which objects will appear to be reasonably sharp) will become shallower.
We filmed 2 videos using a Canon t3i with Magic Lantern firmware and were able to get some stunning results!
The first video was filmed in the souk of Beirut:
The second is a stop-motion shot at night with at least 4 seconds of open exposure and heavy laser play: