We present a novel, quality-driven, architectural-level approach that trades-off the output quality to enable power-aware processing of multimedia streams. The error tolerance of multimedia data is exploited to selectively eliminate computation while maintaining a specified output quality. We construct relaxed, synthesized power macro-models for power-hungry units to predict the cycle-accurate power consumption of the input stream on the fly. The macro-models, together with an effective quality model, are integrated into a programmable architecture that allows both power savings and quality to be dynamically tuned with the available battery-life. In a case study, power monitors are integrated with functional units of the IDCT module of a MPEG-2 decoder. Experiments indicate that, for a moderate power monitor energy overhead of 5%, power savings of 72% in the functional units can be achieved resulting in an increase in battery life by 1.95x.