Variable Bit Rate (VBR) video transmission over UMTS networks is assuming an ever growing importance. To face the problem of VBR data transmission over wireless channels, work-ahead smoothing techniques can be fruitfully adopted. In this work, a sliding window smoothing algorithm, particularly suitable for real-time interactive multimedia transmission of VBR streams is proposed. It smoothes video streams over partially overlapped time windows, taking into account the fluctuating available bandwidth profile, typical of the wireless link, and the feedback on the real available buffer size periodically coming from client terminals, with the aim to minimize losses. Numerical results demonstrate the effectiveness of the proposed algorithm if compared with the sliding version of Minimum Variability Bandwidth Allocation (MVBA) algorithm, already known by literature, in different contexts.