Coherent acoustic waves at ultrahigh frequencies offer opportunities for nanoscale signal processing, sensing and hybrid optomechanical technologies, but their generation and controlled emission beyond the gigahertz regime remain challenging. Here we report optically programmable nanoacoustic sources that emit coherent propagating hypersound at 20~GHz into a semiconductor waveguide at room temperature. The sources are based on optophononic microcavities that confine light and sound vertically while enabling in-plane acoustic emission and transport over distances up to $20\mu$m. The optical pulse train periodically replenishes a phase-locked acoustic field, while in-plane propagation of the acoustic fields enables spatial separation between generation and detection volumes. By independently addressing multiple sources and controlling the relative phase of the emitted acoustic fields through the pump-pulse arrival times, we demonstrate phase-programmable interference of propagating acoustic fields, establishing the coherent primitives required for spatial shaping and synthesis of nanoacoustic waveforms. These results introduce a scalable platform for optically controlled hypersound generation and delivery, opening pathways toward reconfigurable nanoacoustic devices based on optically controlled coherent hypersound fields.