We study convergence of a mixed finite element-finite volume scheme for the compressible Navier Stokes equations in the isentropic regime under the full range of the adiabatic coefficient gamma for the problem with general non zero inflow/outflow boundary conditions. We propose a modification of Karper scheme [Numer. Math. 125:441-510, 2013] in order to accommodate the non zero boundary data, prove existence of its solutions, establish the stability and uniform estimates, derive a convenient consistency formulation of the balance laws and use it to show the weak convergence of the numerical solutions to a dissipative solution with the Reynold defect introduced in Abbatiello et al. [Preprint Arxiv 1912.12896]. If the target system admits a strong solution then the convergence is strong towards the strong solution. Moreover, we establish the convergence rate of the strong convergence in terms of the size of the space discretization h (which is supposed to be comparable with the time step). In the case of non zero inflow/outflow boundary data, all results are new. The latter result is new also for the no-slip boundary conditions.