Why Is HTTP Adaptive Streaming So Hard?

Abstract

HTTP adaptive streaming is increasingly popular in video delivery. This is mainly because HTTP allows easy deployment while it simplifies content delivery, and chunk-based delivery enables dynamic adaptation of video quality to varying network bandwidth. However, we find that the very nature of chunk delivery on HTTP causes some fundamental problems in efficient bandwidth utilization. In this work, we investigate why it is so hard to adapt to varying bandwidth with HTTP adaptive streaming. First, we find that the choice of chunk duration greatly affects the bandwidth adaptation logic. Second, we observe that the disparity between the advertised quality of a chunk and real encoding rate confuses the client-side adaptation logic. Third, the dependence on TCP/HTTP leads to suboptimal bandwidth utilization while it makes it challenging to adapt to rapidly-changing bandwidth. We show the evidence of the problems in our controlled experiments with popular HTTP adaptive streaming schemes, and lay out the future requirements for robust bandwidth adaptation in video streaming.