Context. Main sequence stars with a convective core are predicted to stochastically excite internal gravity waves (IGWs), which effectively transport angular momentum throughout the stellar interior and explain the observed near-uniform interior rotation rates of intermediate-mass stars. However, there are few detections of IGWs, and fewer still made using photometry, with more detections needed to constrain numerical simulations. Aims. We aim to formalise the detection and characterisation of IGWs in photometric observations of stars born with convective cores (M ≳ 1.5 M_⊙) and parameterise the low-frequency power excess caused by IGWs. Methods. Using the most recent CoRoT light curves for a sample of O, B, A and F stars, we parameterised the morphology of the flux contribution of IGWs in Fourier space using an MCMC numerical scheme within a Bayesian framework. We compared this to predictions from IGW numerical simulations and investigated how the observed morphology changes as a function of stellar parameters. Results. We demonstrate that a common morphology for the low-frequency power excess is observed in early-type stars observed by CoRoT. Our study shows that a background frequency-dependent source of astrophysical signal is common, which we interpret as IGWs. We provide constraints on the amplitudes of IGWs and the shape of their detected frequency spectrum across a range of mass, which is the first ensemble study of stochastic variability in such a diverse sample of stars. Conclusions. The evidence of a low-frequency power excess across a wide mass range supports the interpretation of IGWs in photometry of O, B, A and F stars. We also discuss the prospects of observing hundreds of massive stars with the Transiting Exoplanet Survey Satellite (TESS) in the near future.