Broadband access is an important requirement to satisfy user demands and support a new set of real time services and applications. WiMAX, as a Broadband Wireless Access solution for Wireless Metropolitan Area Networks, covering large distances with high throughput and is a promising technology for Next Generation Networks. Nevertheless, for the successful deployment of WiMAX based solutions, Quality of Service (QoS) is a mandatory feature that must be supported. Quality of Service (QoS) is an important consideration for supporting variety of applications that utilize the network resources. These applications include voice over IP, multimedia services, like, video streaming, video conferencing etc. In this paper the performances of the MPEG-4 High quality video traffic over a WiMAX network using various service classes has been investigated. To analyze the QoS parameters, the WiMAX module developed based on popular network simulator NS-3 is used. Various parameters that determine QoS of real life usage scenarios and traffic flows of applications is analyzed. The objective is to compare different types of service classes with respect to the QoS parameters, such as, throughput, packet loss, average delay and average jitter.