MLG is an authoring environment aimed to provide integrated multimedia tools that assist the design and implementation of on-line lessons, realised by the authors in the context of a research contract focussed on the objectives of Information Society R&D direction. Mainly, a lesson presentation is made by means of one or more HTML pages, integrating various multimedia learning objects. The central learning object is an audio/video movie, which leads the whole deployment of the lesson; the movie is built as a data stream, using Windows Media control.