fix(dash): treat a caption subtitle also marked SDH as SDH

tests/core/test_dash_caption_sdh.py

@@ -0,0 +1,19 @@
+import xml.etree.ElementTree as ET
+
+from unshackle.core.manifests.dash import DASH
+
+CAPTION = '<Role schemeIdUri="urn:mpeg:dash:role:2011" value="caption"/>'
+SDH = '<Accessibility schemeIdUri="urn:tva:metadata:cs:AudioPurposeCS:2007" value="2"/>'
+
+
+def test_caption_role_is_closed_caption() -> None:
+    element = ET.fromstring(f"<AdaptationSet>{CAPTION}</AdaptationSet>")
+    assert DASH.is_closed_caption(element) is True
+    assert DASH.is_sdh(element) is False
+
+
+def test_caption_role_with_sdh_value_is_sdh_only() -> None:
+    # a Subtitle cannot be both CC and SDH, so a set marked both used to fail the whole title
+    element = ET.fromstring(f"<AdaptationSet>{CAPTION}{SDH}</AdaptationSet>")
+    assert DASH.is_closed_caption(element) is False
+    assert DASH.is_sdh(element) is True

unshackle/core/manifests/dash.py

@@ -1293,8 +1293,8 @@ class DASH:
 
     @staticmethod
     def is_closed_caption(adaptation_set: Element) -> bool:
-        """Whether the Adaptation Set is a Closed Caption Subtitle."""
-        return any(
+        """Whether the Adaptation Set is a Closed Caption Subtitle. A caption that is also marked SDH counts as SDH."""
+        return not DASH.is_sdh(adaptation_set) and any(
             (x.get("schemeIdUri"), x.get("value")) == ("urn:mpeg:dash:role:2011", "caption")
             for x in adaptation_set.findall("Role")
         )