Wang et al. proposed cross layer resource allocation according to the channel state information of the physical layer and the video rate distortion of the application layer for uplink orthogonal frequency division multiple access (OFDMA) video transmission systems. Its object function is minimizing sum of all users' video distortion. It shows significant improvement in average peak-signal-to-noise-ratio (PSNR) over the schemes which consider either the physical layer or application layer. However, minimizing sum of all users' video distortion does not necessarily maximize average of all users' PSNR. In this paper, we change the objective function for optimization to maximize average PSNR, and derive new optimal condition for cross layer subcarrier assignment for infinitesimal bandwidth increment. Furthermore, we extend to a multi-user multiple-input and multiple-output (MU-MIMO) uplink transmission system to improve information rate and thus video quality. We then propose an average PSNR optimized physical/application cross-layer user grouping and resource allocation for uplink MU-MIMO OFDMA video communications. The simulation results show that the proposed scheme has 4 dB PSNR gain over the previous Wang et al. cross-layer scheme and 5 dB PSNR gain over the previous physical layer only scheme for four users and SNR 12-18 dB.