Placing and moving virtual cameras in real-time 3D environments is a task that remains complex due to the many requirements which need to be satisfied simultaneously. Beyond the essential features of ensuring visibility and frame composition for one or multiple targets, an ideal camera system should provide designers with tools to create variations in camera placement and motions, and create shots which conform to aesthetic recommendations. In this paper, we propose a controllable process that will assist developers and artists in placing cinematographic cameras and camera paths throughout complex virtual environments, a task that was often manually performed until now. With no specification and no previous knowledge on the events, our tool exploits a topological analysis of the environment to capture the potential movements of the agents, highlight linearities and create an abstract skeletal representation of the environment. This representation is then exploited to automatically generate potentially relevant camera positions and trajectories organized in a graph representation with visibility information. At run-time, the system can then efficiently select appropriate cameras and trajectories according to artistic recommendations. We demonstrate the features of the proposed system with realistic game-like environments, highlighting the capacity to analyze a complex environment, generate relevant camera positions and camera tracks, and run efficiently with a range of different camera behaviours.