- If there's no program-date-time then this change is
a no-op.
- If there is a program-date-time this change considers
the period as having started at the epoch rather than
at the start of the content. The window is then set
to start at the start of the content. This is a little
weird, but is required so that the period sample
timestamps match the start of the period. Note that
this also brings the handling of on-demand in line
with how the live case is handled, meaning there wont
be weird changes if a live stream changes into an
on-demand one.
Issue: #2224
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=142442719
ab88821614