In the past few years, scattering amplitude has been proven to be a useful tool to compute observables in classical gravitational systems. In this talk, I will present a recent computation of the next-to-leading order scattering waveform of two uncharged black holes in general relativity and half-BPS black holes in N=8 supergravity. The results are extracted from the one-loop five-point amplitudes involving two massive scalars and a graviton in the final state using the KMOC formalism. We also prove that only two-matter-irreducible graphs contribute to classical exclusive observables. Our result agrees exactly with a heavy particle effective theory calculation, indicating the validity of the latter. Precise waveform models are crucial to the analysis of gravitational wave signals, and I will end the talk by discussing possible extension to bound systems.