Understanding the behavior of light in nonequilibrium scenarios underpins much of quantum optics and optical physics. While lasers provide a severe example of a nonequilibrium problem, recent interests in the near-equilibrium physics of so-called photon gases, such as in Bose condensation of light or in attempts to make photonic quantum simulators, suggest one re-examine some near-equilibrium cases. Here we consider how a sinusoidal parametric coupling between two semi-infinite photonic transmission lines leads to the creation and flow of photons between the two lines. Our approach provides a photonic analog to the Landauer transport formula, and using nonequilbrium Green s functions, we can extend it to the case of an interacting region between two photonic leads where the sinusoid frequency plays the role of a voltage bias. Crucially, we identify both the mathematical framework and the physical regime in which photonic transport is directly analogous to electronic transport and regimes in which other behavior such as two-mode squeezing can emerge.