Issue 912: cmx_3600 adapter incorrectly processing three-clip transit…

…ions (#919)

* Issue #912 - Test for dissolve issue with cmx_3600 adapter
* Issue #912 - Change cmx_3600 adapter for A->B->C Transitions"
* Update src/py-opentimelineio/opentimelineio/adapters/cmx_3600.py

Co-authored-by: jburnell <[email protected]>
Co-authored-by: Stephan Steinbach <[email protected]>

src/py-opentimelineio/opentimelineio/adapters/cmx_3600.py

@@ -627,6 +627,16 @@ def parse(self, comment):
                 self.unhandled.append(stripped)
 
 
+def _get_next_clip(start_index, track):
+    """Get the next clip with a non-zero duration"""
+    # Iterate over the following clips and return the first "real" one
+    for clip in track[start_index + 1:]:
+        if clip.duration().value > 0:
+            return clip
+
+    return None
+
+
 def _expand_transitions(timeline):
     """Convert clips with metadata/transition == 'D' into OTIO transitions."""
 
@@ -635,13 +645,10 @@ def _expand_transitions(timeline):
     replace_or_insert_list = []
     append_list = []
     for track in tracks:
-        track_iter = iter(track)
         # avid inserts an extra clip for the source
         prev_prev = None
         prev = None
-        clip = next(track_iter, None)
-        next_clip = next(track_iter, None)
-        while clip is not None:
+        for index, clip in enumerate(track):
             transition_type = clip.metadata.get('cmx_3600', {}).get(
                 'transition',
                 'C'
@@ -651,8 +658,6 @@ def _expand_transitions(timeline):
                 # nothing to do, continue to the next iteration of the loop
                 prev_prev = prev
                 prev = clip
-                clip = next_clip
-                next_clip = next(track_iter, None)
                 continue
 
             wipe_match = re.match(r'W(\d{3})', transition_type)
@@ -730,6 +735,7 @@ def _expand_transitions(timeline):
 
             # expand the next_clip or contract this clip
             keep_transition_clip = False
+            next_clip = _get_next_clip(index, track)
             if next_clip:
                 if _transition_clips_continuous(clip, next_clip):
                     sr = next_clip.source_range
@@ -771,8 +777,6 @@ def _expand_transitions(timeline):
                 del(new_trx.metadata['previous_metadata'])
 
             prev = clip
-            clip = next_clip
-            next_clip = next(track_iter, None)
 
     for (insert, track, from_clip, to_transition) in replace_or_insert_list:
         clip_index = track.index(from_clip)

tests/sample_data/dissolve_test_4.edl

@@ -0,0 +1,12 @@
+TITLE:   TRANSITION_TEST_2
+FCM: NON-DROP FRAME
+001  ABC0000. V     C        01:00:06:18 01:00:08:00 01:04:11:17 01:04:12:23
+002  ABC0010. V     C        01:00:06:15 01:00:08:18 01:04:12:23 01:04:15:02
+003  ABC0010. V     C        01:00:08:18 01:00:08:18 01:04:15:02 01:04:15:02
+003  ABC0020. V     D    035 01:00:06:22 01:00:10:07 01:04:15:02 01:04:18:11
+* BLEND, DISSOLVE
+004  ABC0020. V     C        01:00:10:07 01:00:10:07 01:04:18:11 01:04:18:11
+004  ABC0030. V     D    064 01:00:06:10 01:00:09:22 01:04:18:11 01:04:21:23
+* BLEND, DISSOLVE
+005  ABC0040. V     C        01:00:08:14 01:00:12:14 01:04:21:23 01:04:25:23
+060  ABC0050. V     C        01:00:12:06 01:00:17:21 01:04:25:23 01:04:31:14

tests/test_cmx_3600_adapter.py

@@ -50,6 +50,7 @@
 DISSOLVE_TEST = os.path.join(SAMPLE_DATA_DIR, "dissolve_test.edl")
 DISSOLVE_TEST_2 = os.path.join(SAMPLE_DATA_DIR, "dissolve_test_2.edl")
 DISSOLVE_TEST_3 = os.path.join(SAMPLE_DATA_DIR, "dissolve_test_3.edl")
+DISSOLVE_TEST_4 = os.path.join(SAMPLE_DATA_DIR, "dissolve_test_4.edl")
 GAP_TEST = os.path.join(SAMPLE_DATA_DIR, "gap_test.edl")
 WIPE_TEST = os.path.join(SAMPLE_DATA_DIR, "wipe_test.edl")
 TIMECODE_MISMATCH_TEST = os.path.join(SAMPLE_DATA_DIR, "timecode_mismatch.edl")
@@ -1047,6 +1048,26 @@ def test_transition_duration(self):
 
         self.assertEqual(tl.tracks[0][2].duration().value, 26.0)
 
+    def test_three_part_transition(self):
+        """
+        Test A->B->C Transition
+        """
+        tl = otio.adapters.read_from_file(DISSOLVE_TEST_4)
+        self.assertEqual(len(tl.tracks[0]), 8)
+
+        self.assertIsInstance(tl.tracks[0][2], otio.schema.Transition)
+        self.assertIsInstance(tl.tracks[0][4], otio.schema.Transition)
+
+        self.assertEqual(tl.tracks[0][2].duration().value, 35.0)
+        self.assertEqual(tl.tracks[0][4].duration().value, 64.0)
+
+        self.assertEqual(tl.tracks[0][0].duration().value, 30.0)
+        self.assertEqual(tl.tracks[0][1].duration().value, 68.0)
+        self.assertEqual(tl.tracks[0][3].duration().value, 96.0)
+        self.assertEqual(tl.tracks[0][5].duration().value, 52.0)
+        self.assertEqual(tl.tracks[0][6].duration().value, 96.0)
+        self.assertEqual(tl.tracks[0][7].duration().value, 135.0)
+
 
 if __name__ == "__main__":
     unittest.main()