Live streaming services over HTTP used on smart devices via a mobile network have become very popular. However, playback interruption often occurs during a live streaming. This is because TCP throughput fluctuates due to radio strength variation and cross-traffic, and the playback buffer on the client side is small. To solve the playback interruption problem, adaptive rate control techniques are helpful. However, using a smart device with insufficient CPU power leads to control delays, which cause the rate to be controlled improperly. This paper proposes a novel rate control method that uses plural codecs and detection of throughput degradation, and shows that the proposed method reduces playback interruptions on smart devices. We evaluate our proposed method with a live streaming for 100 seconds as an experiment in conditions in which the TCP throughput is fluctuated by a network emulator. Playback interruption occurred three times and lasted 1.8 seconds in total with the conventional method, but did not occur with the proposed method. We also evaluate the method from the viewpoint of QoE defined in ITU-T Rec.P.1201/Amd.2. The proposed method is able to improve QoE(MOS) to 3.5 from 2.6 of conventional method.
