Myth.rebuilddatabase.pl allows you to import a video into your recorded table in the mythconverg database.
If the file you would like to import is named TV_Show.avi then run from the contrib directory run.
myth.rebuilddatabase.pl --dir /mythtv/Recorded --ext avi
It will now look in the directory named '/mythtv/Recorded' and for any files with the 'avi' extension. (ie. ll -lh /mythtv/Recorded/*.avi)
After it finds a file it will ask you if you would like to import it into your database and what info you would like to import.