When it comes to noise in photos, we are pretty accustomed to using DeNoising tools. When it comes to video, there are similar options that apply that same logic to footage, rather than to a single frame.
The folks over at Film Riot took two of the more popular options, Neat Video and Denoiser II (both at about $100) for a test drive and compare the results. Ryan talks about a third plugin called Dark Energy which he says surpasses them both, but sadly, it fell of the comparison for costing $100 more.
Now, of course that you may want to get the your footage as noise free as you can in camera, and a workflow sometimes removes the “built in” noise only to digitally add film grain later on.
To avoid noise, use native ISO if you can (or generally low ISO if you can’t). Sometimes, though, especially with low budget DSLR projects you can’t always shoot low ISO so using a denoiser is sometimes your only option for saving a video.
Both Neat Video and Denoiser II look pretty good to me on the test, however commenters indicate that Denoiser II is too slow for some of the projects, while Neat Video provides better tools for fine tuning and profiling noise.