Looks to me that your question results either in huge automatically generated (by Windows) thumbnail file for each movie (at least the size of the original movie) or enormous bite out of the available CPU resources every time you open a folder with these kind of files. And you should hope that those files are not cached else you have one movie (700Mb), one thumbnail file (700Mb) and a cached version (700Mb) on your system, which adds up quickly.
Although I like your idea, it seems a bit impractical (maintenance wise) to me.