A streaming measurement agent designed to experience, measure, and report on a media stream as an actual end user would experience the stream. Preferably, agent resides transparently within a streaming media player itself so that it can monitor stream packet flows within the player as the measured streams are being played. In an illustrative embodiment, the agent comprises a performance monitoring module (PMM), which is software that resides in an interface between an existing core module and a renderer of a media player. The agent PMM intercepts each useful packet as it goes from the core to the renderer and, as a result, it is able to compute quality metrics about the playback. The agent functions "transparently" to the media player by presenting the core with an application programming interface (API) that emulates the API that the renderer normally presents to the core. Thus, when the core believes it is calling the renderer, it is actually calling the agent PMM, which can then receive all the packets from the core and process them. After computing relevant performance metrics using the packets it receives, the agent PMM calls the renderer. A set of performance agents can be managed by a service provider to enable a content provider to determine how a stream is perceived by end users.