Objects and iterators
FileSetFactory returns groups of files in succession. For now FileSetFactory can return 2 types of objects. They respond to the protocol AbstractFileSet, although such a class doesn't exist.
|path||A field (string) than uniquely identify the FileSet. For a SingleFile, this is the file path itself, for a VideoTS, the path to the directory.|
SingleFile is one file, like an image or a .avi video.
VideoTS is a directory containing a VIDEO_TS directory and all the subtree beneath.