PublishTime

Updates of publishTime

The publishTime element at the MPD level is often used as a version control of a dynamic MPD. In particular, in some use cases, like inband signaling of MPD updates and MPD Patch, a PublishTime values are compared to discover a change of MPD change.

In a traditional origin server that continously generates an updated MPD every time a new segment is generated this is straight-forward to achieve.

In livesim2 there is no such continuous process, but all manifests and segments are generated on the fly. There is also the possibility to change the relevant time by adding the ?nowMS=.... parameter in any URL. For that reason, livesim2 calculates a publishTime on any MPD request based on when the last change was done. For an MPD using SegmentTemplate with $Number$ this is typically the availabilityStartTime, or or the start of an added period. The case of SegmentTimeline is more complex. The algorithm used here is to look at the availabilityTime of the last segment in the Manifest and use that to define the publishTime. In case of a non-zero availabilityTimeOffset value, the publishTime is shifted with the same amount to signal that the last segment in the MPD is available that same amount earlier than its end time.

The publishTime value is cropped to millisecond accuracy with trailing zeroes suppressed.