Recent advances in wireless communication have raised possibility of creating new sets of richer multimedia applications in wireless networks; on the other hand, despite the rapid evolution and growing popularity of mobile handheld devices such as PDAs and smart phones, they are still significantly computationally constrained by limited resources for some kind of applications (e.g. computer graphics). The main contribution of this work is the design of a closed-loop controller in the context of image/video streaming systems with interactivity constraints to automatically adapt streaming parameters to bandwidth fluctuations. The proposed technique is general and acts as a sort of Quality of Service (QoS) mechanism at the application level and can be applied to any kind of client, but in this context we point out at common handheld devices, such as PDAs and smart phones, as a target. Experiments were carried out using different encoding standards (M-JPEG and MPEG-4 Part 2) and different network access (802.1 lg and HSDPA).