Fix empty line check

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

@@ -191,7 +191,7 @@ def _make_span(self, parent: model.ContentElement) -> model.Span:
     return span
 
 
-_EMPTY_RE = re.compile(r"\s+")
+_EMPTY_RE = re.compile(r"[\n\r]*")
 _DEFAULT_FONT_STACK = (styles.GenericFontFamilyType.sansSerif,)
 _DEFAULT_FONT_SIZE = styles.LengthType(15 * 5, styles.LengthType.Units.pct) # 5vh for ttp:cellResolution="32 15"
 _DEFAULT_TEXT_COLOR = styles.NamedColors.white.value
@@ -451,7 +451,6 @@ class _State(Enum):
 
   state = _State.START
   current_p = None
-  subtitle_text = None
 
   for line_index, line in enumerate(_none_terminated(lines)):
 
@@ -519,7 +518,7 @@ class _State(Enum):
       current_p.set_region(_get_or_make_region(doc, cue_params[3:]))
 
       state = _State.TEXT
-
+      subtitle_text = None
       continue
 
     if state in (_State.TEXT, _State.TEXT_MORE):
@@ -535,7 +534,6 @@ class _State(Enum):
           LOGGER.warning("Ignoring cue due to a spurious blank line at line %s", line_index)
 
         state = _State.LOOKING
-        subtitle_text = None
         continue
 
       if state is _State.TEXT:

src/test/python/test_vtt_reader.py

@@ -119,6 +119,28 @@ def test_malformed_blank_lines(self):
     div = list(body[0])
     self.assertEqual(len(div), 1)
 
+  def test_single_line_with_space(self):
+    # from https://github.com/sandflow/ttconv/issues/439
+    # the first cue is not ignored since the first line contains a single space
+    SAMPLE = """WEBVTT
+Kind: captions
+Language: en
+
+00:00:00.799 --> 00:00:02.869 align:start position:0%
+ 
+hi<00:00:01.040><c> everyone</c><00:00:01.920><c> today</c><00:00:02.240><c> we're</c><00:00:02.399><c> going</c><00:00:02.639><c> to</c><00:00:02.720><c> be</c>
+
+00:00:02.869 --> 00:00:02.879 align:start position:0%
+hi everyone today we're going to be
+"""
+
+    doc = to_model(io.StringIO(SAMPLE))
+    self.assertIsNotNone(doc)
+    body = list(doc.get_body())
+    self.assertEqual(len(body), 1)
+    div = list(body[0])
+    self.assertEqual(len(div), 2)
+
   def test_italic(self):
     f = io.StringIO(r"""WEBVTT