The buffer/slack amount (seconds) actually reserved past the live edge as of the last time it
was resolved — the static TimelineConfig.liveEdgeBufferSpace when no TimelineConfig.liveEdgeBufferSpaceUpdate is configured (or it hasn't produced a value yet), or
whatever TimelineConfig.liveEdgeBufferSpaceUpdate last resolved to otherwise. Unlike the
static config value, this can change over the life of the timeline. undefined when neither is
configured (no buffer reserved at all).
How much of liveEdgeBufferSpace is still unconsumed right now — the gap between liveExtentEnd and the current live edge. Shrinks as manifest growth is absorbed without a
reflow, and resets back to the full liveEdgeBufferSpace on the next reflow. undefined
when liveEdgeBufferSpace isn't configured or the timeline isn't live.
Right edge of the live coordinate domain (media-element-absolute time), including any reserved locked region.
Whether the timeline is currently rendering live media. When false, the other live-only fields are meaningless.