In this paper, we consider multimedia Quality-of-Service (QoS) in resource constrained embedded systems, where scalable applications are structured as directed acyclic graphs of tasks, which communicate via shared buffers. Scalable multimedia applications allow to trade quality for resource usage during run-time. We present two QoS problems: (i) temporal dependencies between subchains of tasks due to a common predecessor, and (ii) mode change latency in applications. These problems are addressed through advanced memory management techniques. For the first problem, it is shown how additional access to the buffer, in particular the support for dropping selected frames, allows to guarantee the Quality of Service of the application during overload conditions, preventing congestion in one buffer to propagate across the whole application. For the latter problem, the approach of in-buffer scaling is applied to reduce the mode change latency in scalable multimedia processing applications, which can adapt their memory requirements during runtime according to a set of predefined modes. The latter approach is validated with simulation results.