In this paper, real-time video transmission with quality of service (QoS) assurance over orthogonal frequency division multiplexing (OFDM) wireless systems is studied. Three quasi-optimal subcarrier allocation schemes, namely regular, delay tolerant and adaptive, are proposed. In the proposed schemes, effective throughput per subcarrier employing adaptive forward error correction (FEC) coding in a Rayleigh fading channel is evaluated, and a capacity matrix that governs all active users and all assignable subcarriers is formulated. The Munkres algorithm is used in the schemes to achieve optimal subcarrier assignment. Performance analyses in terms of spectral efficiency and packet loss probability are presented. Multi-user multichannel diversity is investigated to exploit the innate capacity gain in terms of fading variation and delay tolerance. The proposed schemes are scalable to both single-cell and multi-cell circumstances. Numerical results demonstrate that the proposed schemes can effectively achieve quasi-optimal spectral utilization and significantly improve system throughput.