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This paper presents an intra-fame rate control algorithm for ultralow delay H.264/AVC coding. The main goal of the proposed scheme is to allocate a proper bit budget to each macroblock (MB), based on its complexity (or activity). However, since a coder needs to start encoding a frame before buffering the whole frame for very low delay video streaming applications, the relative complexity of each MB can not be known in advance. So, the proposed algorithm predicts a relative complexity of a current MB from complexities of its spatially/temporally neighboring MBs, and then allocates a proper bit budget to the MB using the predicted complexity. Finally, quantization parameter of each MB is obtained by comparing the generated bits and allocated bit budget, and is refined for improving coding performance, based on information from the previous frame. Even though the required buffer size is only around one-third of average bits per a frame in order to achieve very low coding delay, the proposed algorithm provides reliable coding performance compared to the conventional schemes. Simulation results show that the proposed algorithm can prevent the buffer overflow or underflow and it provides better coding performance.