@rmsint is the lead of MediaBundle. basically its just interfaces and phpcr-odm model classes for folders, files and images. it does very little of its own in the end - more of a glue between phpcr-odm, liipimagine, elfinder for image selection and hopefully soon also sonata. SonataMediaBundle has a very complex offer for managing media from cdn, on vimeo and so on, editing images in the browser useing some javascript based external service and whatnot. but i don't know if it can be used without SonataAdminBundle.