Open Caching Request Routing Functional Specification (Version 2.0)
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There are a number of different methods by which rewrites can be handled in-session. One of those methods, manifest rewrites, was not included in the original Open Caching Request Routing specification. The specification needed to be updated to address this common rewrite technique for segmented HLS streaming video.
With Manifest rewrite, a video platform can change the URLs for individual segments by rewriting the manifest. This works best with HLS which has complete URLs for each segment in the media playlists, so any segment can be pointed to any source. For live, the segment list is fetched again by the client as new segments are created, and a server can change the latest segment to point to an alternate source (such as another CDN) the segments were not pointing at before. This effectively moves clients to the new source in a controlled fashion. However, this requires an explicit list of URLs and, thereby, does not work with DASH which uses the same URL for all segments in a bitrate variant. Changing the manifest during the session does not work for VoD either, since the manifest or playlist is only downloaded once when the stream is initialized which results in all segment requests being directed to the CDN, or CDNs, decided at the start of the session. Manifest rewrite can be used to redirect part of the traffic to a separate server with diagnostic capabilities and collect server side metrics to gain insights into the session.
March 1, 2019
Estimated Completion Date
March 6, 2020
Goals and Objectives
This project has the following goals and objectives:
- To update the Version 1.1 Open Caching Request Routing Functional Specification document to Version 2.0 which will include details on how the Open Caching system can make use of the Manifest Rewrite method
The document produced by this project will PROVIDE:
- An updated Request Routing Functional Specification document which includes the Manifest Rewrite method
- Any additional updates to the Request Routing Functional Specification
The following members have contributed to this document:
- Matt Stock (Limelight Networks)
The following references can help project participants gain a better understanding of Open Caching and Manifest Rewrites: