Dynamic adaptation of HTTP-based video streaming using Markov decision process

摘要

Hypertext transfer protocol (HTTP) is the fundamental mechanics supporting web browsing on the Internet. An HTTP server stores large volumes of contents and delivers specific pieces to the clients when requested. There is a recent move to use HTTP for video streaming as well, which promises seamless integration of video delivery to existing HTTP-based server platforms. This is achieved by segmenting the video into many small chunks and storing these chunks as separate files on the server. For adaptive streaming, the server stores different quality versions of the same chunk in different files to allow real-time quality adaptation of the video due to network bandwidth variation experienced by a client. For each chunk of the video, which quality version to download, therefore, becomes a major decision-making challenge for the streaming client, especially in vehicular environment with significant uncertainty in mobile bandwidth. The key objective of this thesis is to explore more advanced decision making tools that would enable an improved tradeoff between conflicting QoE metrics in vehicular environments. In particular, this thesis studies the effectiveness of Markov decision process (MDP), which is known for its ability to optimize decision making under uncertainty. The thesis makes three fundamental contributions: (1) using real video and network bandwidth datasets, it shows that MDP can reduce playback deadline miss of the video (video freezing) by up to 15 times compared to a well known non-MDP strategy when the bandwidth model is known a priori, (2) it proposes a Q-learning implementation of MDP that does not need any a priori knowledge of the bandwidth, but learns optimal decision making in a self-learning manner by simply observing the outcome of its decision making. It is demonstrated that, in terms of deadline miss, the Q-learning-based MDP outperforms the model-based MDP by a factor of three, and (3) it implements the proposed decision making framework in an Android framework and demonstrates the effectiveness of the proposed MDP-based video adaptation through real experiments.