A non-video frame can reach the muxer after the video that opened the next
epoch has already been processed. It carries an old-epoch PTS, so adding
the new offset flings it forward by a whole clip. The remap that exists to
catch this compared the frame against the CURRENT frontier and only
accepted it within one backstep, which is the wrong yardstick: by the time
a straggler is seen the frontier has moved on into a new epoch, and how far
below it the frame lands says nothing about where it belongs.
Retiring an epoch now records the frontier it closed at alongside its
offset, and a straggler is judged against the end of the epoch its PTS came
from. Keeping the whole history rather than one previous offset also fixes
the case a single `prev_offset_ns` cannot express at all: a frame from two
or more epochs back.
Measured on a real HD-DVD title whose second audio track put its final
packet at 12834.587 s in a 6434.100 s file. That frame sits 23 s below the
current frontier — outside the old window, so it was refused — but 0.15 s
below the end of the clip it actually came from. It now lands at 6417.216,
one 32 ms cadence step after its neighbour, and the track spans 6416.160
with no outsized gaps. The other two streams are unchanged.
A title that never rebases retires no epoch, so the lookup finds nothing
and the mapping is bit-identical to before.
Matthew Jackson
70e1807e61