Support nested audio dissolve

Only look for slot index if parent is mobslot

Signed-off-by: Mark Reid <mindmark@gmail.com>

src/otio_aaf_adapter/adapters/advanced_authoring_format.py

@@ -618,7 +618,9 @@ def _transcribe(item, parents, edit_rate, indent=0):
             ]
             timeline_slot = timeline_slots[-1]
             if timeline_slot:
-                metadata["PhysicalTrackNumber"] = list(parent.slots).index(item) + 1
+                if hasattr(parent, 'slots'):
+                    slot_index = list(parent.slots).index(item) + 1
+                    metadata["PhysicalTrackNumber"] = slot_index
                 metadata["SlotID"] = int(timeline_slot["SlotID"].value)
 
         for component in item.components:

tests/test_aaf_adapter.py

@@ -219,6 +219,11 @@
     SAMPLE_DATA_DIR,
     "bad_marker_track_from_avid.aaf"
 )
+NESTED_AUDIO_DISSOLVE_PATH = os.path.join(
+    SAMPLE_DATA_DIR,
+    "nested_audio_dissolve.aaf"
+)
+
 
 try:
     lib_path = os.environ.get("OTIO_AAF_PYTHON_LIB")
@@ -1258,6 +1263,37 @@ def test_aaf_marker_with_bad_track(self):
 
         self.assertIsNotNone(timeline)
 
+    def test_aaf_nested_audio_dissolve(self):
+        timeline = None
+
+        try:
+            timeline = otio.adapters.read_from_file(
+                NESTED_AUDIO_DISSOLVE_PATH
+            )
+
+        except Exception as e:
+            print('[ERROR] Transcribing test sample data `{}` caused an exception: {}'.format(  # noqa
+                os.path.basename(NESTED_AUDIO_DISSOLVE_PATH),
+                e)
+            )
+
+        self.assertIsNotNone(timeline)
+        track = timeline.tracks[0]
+
+        clip = track[0]
+        self.assertIsInstance(clip, otio.schema.Clip)
+        self.assertEqual(clip.source_range.duration.to_frames(), 43)
+
+        transition = track[1]
+        self.assertIsInstance(transition, otio.schema.Transition)
+        self.assertEqual(transition.duration().to_frames(), 3)
+        self.assertEqual(transition.in_offset.to_frames(), 3)
+        self.assertEqual(transition.out_offset.to_frames(), 0)
+
+        gap = track[2]
+        self.assertIsInstance(gap, otio.schema.Gap)
+        self.assertEqual(gap.source_range.duration.to_frames(), 0)
+
     def _verify_user_comments(self, aaf_metadata, expected_md):
 
         self.assertTrue(aaf_metadata is not None)