fix(dash): number SegmentTimeline segments from startNumber

Timeline manifests with startNumber between 2 and the segment count capped the range at the count, truncating live replays.

tests/core/test_dash_segment_numbering.py

@@ -0,0 +1,63 @@
+"""Segment numbering must start at ``startNumber`` and cover every segment, in both
+``SegmentTemplate`` forms: an explicit ``SegmentTimeline``, and a fixed segment duration."""
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from unshackle.core.manifests.dash import DASH
+from unshackle.core.utils.xml import load_xml
+
+TIMELINE_MPD = """
+<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" type="static" mediaPresentationDuration="PT10S">
+  <Period id="0" start="PT0S">
+    <AdaptationSet mimeType="video/mp4">
+      <SegmentTemplate timescale="1" media="v/$Number$.mp4" startNumber="{start}">
+        <SegmentTimeline><S t="0" d="1" r="{repeat}"/></SegmentTimeline>
+      </SegmentTemplate>
+      <Representation id="v" bandwidth="1"/>
+    </AdaptationSet>
+  </Period>
+</MPD>
+"""
+
+# github.com/unshackle-dl/unshackle/issues/37: 96.72s at 6s per segment is 17 segments, 0 to 16, never a segment 17.
+DURATION_MPD = """
+<MPD xmlns="urn:mpeg:dash:schema:mpd:2011" type="static" mediaPresentationDuration="PT{seconds}S">
+  <Period id="0" start="PT0S" duration="PT{seconds}S">
+    <AdaptationSet mimeType="video/mp4">
+      <SegmentTemplate timescale="25" duration="150" media="v/$Number$.mp4" startNumber="{start}"/>
+      <Representation id="v" bandwidth="1"/>
+    </AdaptationSet>
+  </Period>
+</MPD>
+"""
+
+
+def _numbers(mpd: str) -> list[int]:
+    tree = load_xml(mpd.encode())
+    period = tree.find("Period")
+    aset = period.find("AdaptationSet")
+    rep = aset.find("Representation")
+    _, segments, _, _, _ = DASH.get_period_segments(
+        period, aset, rep, tree, MagicMock(), "https://example.com/main.mpd", MagicMock()
+    )
+    return [int(url.rsplit("/", 1)[1].split(".")[0]) for url, _ in segments]
+
+
+@pytest.mark.parametrize(
+    ("start", "count"),
+    [
+        (0, 5),  # zero-based numbering
+        (1, 5),  # plain VOD
+        (2642, 4667),  # DVR catch-up: startNumber below segment count
+        (5000, 10),  # DVR catch-up: startNumber above segment count
+    ],
+)
+def test_timeline_numbers_follow_start_number(start: int, count: int) -> None:
+    assert _numbers(TIMELINE_MPD.format(start=start, repeat=count - 1)) == list(range(start, start + count))
+
+
+@pytest.mark.parametrize(("start", "seconds", "count"), [(0, "1M36.720", 17), (1, "1M36.720", 17), (2642, "30", 5)])
+def test_duration_numbers_follow_start_number(start: int, seconds: str, count: int) -> None:
+    assert _numbers(DURATION_MPD.format(start=start, seconds=seconds)) == list(range(start, start + count))

unshackle/core/manifests/dash.py

@@ -830,9 +830,6 @@ class DASH:
                         current_time += int(s.get("d"))
 
                 if not end_number:
-                    end_number = len(segment_durations)
-                # Handle high startNumber in DVR/catch-up manifests where startNumber > segment count
-                if start_number > end_number:
                     end_number = start_number + len(segment_durations) - 1
 
                 for t, n in zip(segment_durations, range(start_number, end_number + 1)):