Audio-video streaming in Wi-Fi (IEEE 802.11) wireless local area networks (WLANs) has recently attracted a lot of attention. In order to increase the granularity of traffic prioritization and quality of service (QoS) support defined by EDCA, intra-access category prioritization has recently been introduced in the IEEE 802.11aa amendment. In this paper, we present novel results which show how the new mechanism impacts the performance of an access point (AP). Additionally, we propose a wireless credit-based shaper algorithm (WCBSA), a version of CBSA adjusted to the wireless environment. We also analyze how the different settings of WCBSA impact the prioritization of traffic streams. Finally, we compare the operation of 802.11aa intra-access category prioritization with the legacy inter-access category prioritization defined by EDCA.