Variable bitrate (“VBR”)-based applications may use physical layer metrics, associated with a radio access network (“RAN”), in order to select a data rate and/or codec at which to send and/or receive data. Such VBR-based applications may include voice call application, video streaming applications, or the like. An application programming interface (“API”) between the physical layer and the application layer of a user device may facilitate the analysis of the physical layer metrics of the RAN. The RAN may also, or alternatively, provide physical layer metrics to the user device (e.g., via control signaling). The RAN may enforce constraints on maximum or minimum data rates, and/or may specify codecs that should be used.