Fix: SCC reader skips captions without Preamble Address Code

src/main/python/ttconv/scc/reader.py

@@ -455,7 +455,7 @@ def process_text(self, word: str, time_code: SmpteTimeCode):
       self.active_caption.get_current_text().add_style_property(StyleProperties.FontStyle, self.current_font_style)
       self.active_caption.get_current_text().add_style_property(StyleProperties.TextDecoration, self.current_text_decoration)
 
-    else:
+    elif self.buffered_caption is not None:
       self.buffered_caption.append_text(word)
 
       self.buffered_caption.get_current_text().add_style_property(StyleProperties.Color, self.current_color)
@@ -504,6 +504,10 @@ def process_line(self, line: SccLine) -> SmpteTimeCode:
         spec_char = SccSpecialCharacter.find(scc_word.value)
         extended_char = SccExtendedCharacter.find(scc_word.value)
 
+        if pac is None and self.buffered_caption is None and self.active_caption is None:
+          LOGGER.warning(f"Uninitialized caption: skip {hex(scc_word.value)} code.")
+          continue
+
         if pac is not None:
           debug += "[PAC|" + str(pac.get_row()) + "|" + str(pac.get_indent())
           if pac.get_color() is not None:
@@ -541,7 +545,7 @@ def process_line(self, line: SccLine) -> SmpteTimeCode:
         elif extended_char is not None:
           if self.current_style in (SccCaptionStyle.PaintOn, SccCaptionStyle.RollUp):
             self.active_caption.get_current_text().backspace()
-          else:
+          elif self.buffered_caption is not None:
             self.buffered_caption.get_current_text().backspace()
 
           word = extended_char.get_unicode_value()

src/test/python/test_scc_reader.py

@@ -250,6 +250,59 @@ def test_scc_pop_on_content_unexpectedly_ended(self):
                        "consectetur adipiscing elit.")
     self.assertEqual(region_1, p_list[0].get_region())
 
+  def test_scc_pop_on_content_without_preamble_address_code(self):
+    import logging
+    logging.basicConfig(level=logging.DEBUG)
+
+    scc_content = """\
+Scenarist_SCC V1.0
+
+00:00:02:16	942c
+
+00:00:03:01	9420 91ae 9421 4c6f 7265 6d20 6970 7375 6d20 9220 942c 942f
+
+00:00:07:29	9420 94D0 646f 6c6f 7220 7369 7420 616d 6574 2c80 9470 636f 6e73 6563 7465 7475 7220 6164 6970 6973 6369 6e67 2065 6c69 742e 942c 942f
+
+00:00:09:07	9420 656e 7465 7371 7565 2069 6e74 6572 6475 6d20 6c61 6369 6e69 6120 736f 6c6c 6963 6974 7564 696e 2e80 942c 942f
+
+00:00:11:27	9420
+"""
+
+    scc_disassembly = """\
+00:00:02:16	{EDM}
+00:00:03:01	{RCL}{I}{BS}Lorem ipsum Á{EDM}{EOC}
+00:00:07:29	{RCL}{1400}dolor sit amet,{1500}consectetur adipiscing elit.{EDM}{EOC}
+00:00:09:07	{RCL}entesque interdum lacinia sollicitudin.{EDM}{EOC}
+00:00:11:27	{RCL}
+"""
+
+    self.assertEqual(scc_disassembly, to_disassembly(scc_content))
+
+    doc = to_model(scc_content)
+    self.assertIsNotNone(doc)
+
+    region_1 = doc.get_region("pop1")
+    self.assertIsNotNone(region_1)
+    self.check_region_origin(region_1, 4, 15, doc.get_cell_resolution())
+    self.check_region_extent(region_1, 28, 2, doc.get_cell_resolution())
+    self.check_element_style(region_1, StyleProperties.DisplayAlign, DisplayAlignType.before)
+    self.check_element_style(region_1, StyleProperties.ShowBackground, ShowBackgroundType.whenActive)
+
+    body = doc.get_body()
+    self.assertIsNotNone(body)
+
+    div_list = list(body)
+    self.assertEqual(1, len(div_list))
+    div = div_list[0]
+    self.assertIsNotNone(div)
+
+    p_list = list(div)
+    self.assertEqual(1, len(p_list))
+
+    self.check_caption(p_list[0], "caption1", "00:00:08:26", None, "dolor sit amet,", Br,
+                       "consectetur adipiscing elit.")
+    self.assertEqual(region_1, p_list[0].get_region())
+
   def test_2_rows_roll_up_content(self):
     scc_content = """\
 Scenarist_SCC V1.0