We describe a comment generation subsystem developed as part of an expert authoring system for sail racing scenarios. The result of the expert system analysis is sent to a multimedia presentation subsystem composed of a 3D player and a speaker agent. Comments output by the text-to-speech component must be carefully generated so that they are concise, relevant, non repetitive and timely since they must be synchronized with the 3D animation. The comment generation process is adaptive with respect to the time available and to the user profile and preferences.