By Alexander Giladi, Comcast
In typical linear adaptive streaming deployments, much thought is given to bitrate optimization, in order to maximize a viewer’s quality of experience. The non-negligible overhead of the manifest traffic is, however, typically overlooked. A manifest contains information essential for streaming a video asset, identifying the contents of the stream and the location of where constituent components, like URLs, can be found. A manifest which is frequently refreshed can significantly impact bandwidth consumption and number of requests made to Content Delivery Networks (CDNs). This is true for both Apple® HLS and MPEG DASH streaming systems. While the “manifest bloat” problem is endemic for both systems, this paper concentrates on MPEG DASH and DASH-specific tools. In the case of MPEG DASH, there are several major sources contributing to manifest growth, such as the number of included content periods and the sheer volume of DRM license information. Frequent requests further compound the burden of what is essentially “manifest bloat.” Altogether the manifest overhead can easily reach 250Kbps and go past 2Mbps in some pathologic cases. These numbers are well beyond the typical low-rate video bitrate.