For windows computers you can add a little basic info simply by right clicking the file and choosing properties. However I think it varies by file type of how much info you can add.
Also you could try using mpchc or vlc. They may have the ability to add details to the files. They play most video and audio files but I never tried to add descriptions with them - could be possible.
Edit - you might also try makemkv. It can create mkv files but it might also let you edit descriptions on existing mkv files. Worth a shot.