SPAT-SCENE is a graphical user interface and spatial sound processor embedded in computer-aided composition software. It combines the interface and the rendering engine of Ircam Spatialisateur with a compositional and temporal control of spatial scene descriptors. Previous studies of the composition process as well as interviews with the composers themselves emphasized the needs for tools integrated within compositional environments allowing for interactive input, visualization and manipulation of spatio-temporal data in spatial scene descriptions. The SPAT-SCENE interface addresses such requirements by providing a timeline view synchronized with the spatial view of the Spatialisateur, three-dimensional editors as well as several internal and external rendering possibilities, all in a unified framework. SPAT-SCENE is implemented in the OpenMusic visual programming language, and so can be articulated with other musical structures and compositional processes. Through the case study of sound spatialization, this work tackles the challenge of authoring real-time processes in a compositional context.