If you’ve shot any reasonable amount of video with the 5D Mark II, then you have likely encountered aliasing and moiré pattern interference. Mosaic Engineering has built a filter that fits inside the Canon 5D Mark II and actually fixes these problems.
While there are some other niggling issues created by the use of this filter, it appears that the benefits more than outweigh the problems. Check out the video below for the full rundown.
Right now the filter is only available for the 5D Mark II; however, the company is currently exploring development for the Canon 7D as well.