As video traffic has dominated the data flow of smartphones, traditional cellular communications face substantial transmission challenges. In this work, we study mobile device-to-device (D2D) video distribution that leverages the storage and communication capacities of smartphones. In such a mobile distributed framework, D2D communication represents an opportunistic process to selectively store and transmit local videos to meet the future demand of others. The performance is measured by the service time, which denotes the elapsed period for fulfilling the demand, and the corresponding implementation of each device depends on the video’s demand, availability, and size. The main contributions of this work lie in (1) considering the impact of video size in a practical mobile D2D video distribution scenario and proposing a general global estimation of the video distribution based on limited and local observations; (2) designing a purely distributed D2D video distribution scheme without the monitoring of any central controller; and (3) providing a practical implementation of the scheme, which does not need to know the video availability, user demand, and device mobility. Numerical results have demonstrated the efficiency and robustness of the proposed scheme.