In this paper a problem of finding optimal buffer filling strategy in form of mixed strategy was considered for P2P-TV networks. In such networks, the popularly used strategies are the Rarest First (RF) and Greedy (Gr) strategies, however, studies have shown that RF strategy outperforms Gr strategy in terms of playback continuity and Gr strategy outperforms RF strategy in terms of startup delay, hence there is a need to find an optimal buffer filling strategy inform of mixed strategy with which viewers will experience better playback continuity with short startup delay. The idea of the mixed strategy is to divide the buffer with total of M buffer positions into two parts via demarcation point x, and apply one strategy to fill one part of the buffer and then the other strategy is applied to fill the other part of the buffer. For M = 40 buffer positions, an optimal demarcation point x* was found for each of the proposed mixed strategies. The results of the analysis have shown that mixed strategy where RF is firstly applied for buffer positions from m = 0,…,10, then Gr for m = 11,…,39 is the optimal strategy, with high probability of playback continuity and very low startup delay.