The concept of a critical nucleus size (r*) is of pivotal importance in phase transformations involving nucleation and growth. The current investigation pertains to crystallization in nanoscale thin films and study of the same using high resolution lattice fringe imaging (HRLFI) and finite element simulations. Using the CuZrAl bulk metallic glass system as a model system for this study, we demonstrate a liquid like nucleation behaviour in nanoscale free-standing films upon heating. The r* for the formation of the Cu10Zr7 phase in thin films (of decreasing thickness) approaches that of the r* for the formation of the crystal from a liquid (i.e.). Working in the nucleation dominant regime, we introduce the concept of 'depth sensitive lattice fringe imaging'. The thickness of the film is determined by electron energy loss spectroscopy and the strain energy of the system is computed using finite element computations.