This paper studies the problem of analyzing and designing optimal playout adaptation policies for packet video receivers (PVRs) that operate in a delay jitter inducing best-effort network, like the current Internet. The developed system model is built around the E_k/D_i/1/N phase-type queue and allows for the effective modeling of key design and system parameters, such as: the level of delay jitter, the performance metrics and the employed playout policy. The optimal playout policy is derived under k-Erlang interarrivals by formulating and solving an optimization problem. The (theoretical) optimal solution is transformed into an approximately optimal one that utilizes observable information and it is, thus, feasible. Numerical results are derived under the optimal policy and compared against those under the optimal policy that assumes a fixed level of jitter as determined by Poisson arrivals, as well as against the deterministic service that applies no playout adaptation. Based on this work, a PVR is proposed that adapts to varying network delay jitter and tries to induce a performance that approximates the derived theoretical optimal one.