This letter presents an analytical model that jointly exploits the buffer dynamics of both the sending and receiving nodes to find the optimum number of byte-level and packet-level forward errorcorrection (FEC) units for real-time multimedia transmission over wireless networks. The proposed analytical model first provides an optimum number of FEC units required at the byte-level, and then chooses the number of FEC units at the packet-level based on current channel and network conditions. The accuracy of the proposed model is dependent on two parameters: the variable deadline-time at the byte-level and fixed round-trip time (RTT) delay at the packet-level. Numerical results demonstrate the effectiveness of the model in reducing the unrecoverable error probability, which is achieved when the byte-level FEC scheme is supplemented by the packet-level FEC scheme.