An adaptive rate control for faster bitrate shaping in x264 based video conferencing

In most video streaming applications the available bandwidth may vary during transmission due to the shared nature of IP networks. For efficient bandwidth utilization and in order to manage network congestions, the outgoing bitrate of a streaming application should adapt to changes in network traffic. Current encoders have no strategy for acting in response to bitrate variations that occur as a result of changes in network condition. The time it takes to adapt has a significant impact on the received video quality. A slower response means that more packets are dropped by the network, which in turn results in a lower video quality. Furthermore, a slower response makes the congestion to persist for a longer period of time. In this paper an improved adaptive rate control algorithm for the x264 encoder has been proposed. The proposed scheme is able to adapt the bitrate, by considering the available network capacity, much faster than the conventional method. Simulation results indicate that the proposed algorithm is able to adjust to a bitrate in less than 15 frames, where as it takes more than 42 frames for the conventional method to reach the same bitrate. Consequently, the proposed scheme has no quality degradation or packet loss in %83 of test cases where the bitstream has been exposed to various network conditions, while the conventional rate control reduces quality to 24.02 dB in average in all test cases but one. This improved performance has been achieved with minimum added computational complexity.