We present an experimental study of a gate-defined Quantum Point Contact (QPC) made on a high-mobility, ballistic graphene device. Unlike usual 2D electron gases that can be fully depleted by electrostatic gating, the semi-metal character of graphene leads to the formation of transparent p-n junctions beneath the gates that do not significantly modify the electron transport. In this talk I will show that, when the graphene is turned into the quantum Hall regime, it is possible to use the p-n junction as a guide for quantum Hall edge channels and therefore confine the electron transport into the QPC. Varying the split gate potential of the QPC indeed enables a continuous selection of the transmitted integer as well as fractional edge channels through the constriction. I will then discuss peculiarities occurring in the N=0 Laudau level, which await further theoretical inputs.