WebVTT writer: add support for 'align' (proposed fix)

README.md

@@ -191,6 +191,14 @@ Default: `true`
 
 Default: `false`
 
+#### text_align
+
+`"text_align" : true | false`
+
+`true` means that the VTT writer outputs text alignment cue settings
+
+Default: `false`
+
 #### cue_id
 
 `"cue_id" : true | false`

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

@@ -41,5 +41,8 @@ def name(cls):
   # outputs `line` and `line alignment` cue settings
   line_position: bool = field(default=False, metadata={"decoder": bool})
 
+  # outputs `text alignment` cue settings
+  text_align: bool = field(default=False, metadata={"decoder": bool})
+
   # outputs cue identifier
   cue_id: bool = field(default=True, metadata={"decoder": bool})

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

@@ -42,6 +42,12 @@ class LineAlignment(Enum):
     center = "center"
     end = "end"
 
+  class TextAlignment(Enum):
+    """WebVTT text alignment cue setting"""
+    left = "left"
+    center = "center"
+    right = "right"
+
   _EOL_SEQ_RE = re.compile(r"\n{2,}")
 
   def __init__(self, identifier: Optional[int] = None):
@@ -50,7 +56,8 @@ def __init__(self, identifier: Optional[int] = None):
     self._end: Optional[ClockTime] = None
     self._text: str = ""
     self._line: int = None
-    self._align: VttCue.LineAlignment = None
+    self._linealign: VttCue.LineAlignment = None
+    self._textalign: VttCue.TextAlignment = None
 
   def set_begin(self, offset: Fraction):
     """Sets the paragraph begin time code"""
@@ -83,11 +90,15 @@ def get_line(self) -> Optional[int]:
 
   def set_align(self, align: LineAlignment):
     """Sets the WebVTT line alignment cue setting"""
-    self._align = align
+    self._linealign = align
 
   def get_align(self) -> Optional[LineAlignment]:
     """Return the WebVTT line alignment cue setting"""
-    return self._align
+    return self._linealign
+
+  def set_textalign(self, textalign: TextAlignment):
+    """Sets the WebVTT text alignment cue setting"""
+    self._textalign = textalign
 
   def is_only_whitespace_or_empty(self):
     """Returns whether the paragraph text contains only whitespace or is empty"""
@@ -123,12 +134,16 @@ def __str__(self) -> str:
     # cue timing
     t += f"{self._begin} --> {self._end}"
 
+    # cue text position
+    if self._textalign is not None:
+      t += f" align:{self._textalign.value}"
+
     # cue line position
     if self._line is not None:
       t += f" line:{self._line}%"
 
-      if self._align is not None:
-        t += f",{self._align.value}"
+      if self._linealign is not None:
+        t += f",{self._linealign.value}"
 
     t += "\n"
 

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

@@ -39,7 +39,8 @@
 from ttconv.isd import ISD
 from ttconv.vtt.cue import VttCue
 from ttconv.vtt.css_class import CssClass
-from ttconv.style_properties import ExtentType, PositionType, StyleProperties, FontStyleType, NamedColors, FontWeightType, TextDecorationType, DisplayAlignType
+from ttconv.style_properties import DirectionType, ExtentType, PositionType, StyleProperties, FontStyleType, NamedColors, \
+                                    FontWeightType, TextDecorationType, DisplayAlignType, TextAlignType
 
 LOGGER = logging.getLogger(__name__)
 
@@ -84,7 +85,13 @@ def __init__(self, config: VTTWriterConfiguration):
         StyleProperties.DisplayAlign: [],
         StyleProperties.Extent: [],
       })
-
+
+    if self._config.text_align:
+      supported_styles.update({
+        StyleProperties.TextAlign: [],
+        StyleProperties.Direction: [],
+      })
+
     self._filters.append(SupportedStylePropertiesFilter(supported_styles))
 
     self._filters.append(
@@ -175,6 +182,16 @@ def process_p(self, region: ISD.Region, element: model.P, begin: Fraction, end:
         cue.set_line(round(position.v_offset.value + extent.height.value / 2))
         cue.set_align(VttCue.LineAlignment.center)
 
+    if self._config.text_align:
+      direction = element.get_style(StyleProperties.Direction)
+      text_align = element.get_style(StyleProperties.TextAlign)
+      if text_align == TextAlignType.center:
+        cue.set_textalign(VttCue.TextAlignment.center)
+      elif text_align == TextAlignType.start:
+        cue.set_textalign(VttCue.TextAlignment.right if direction == DirectionType.rtl else VttCue.TextAlignment.left)
+      elif text_align == TextAlignType.end:
+        cue.set_textalign(VttCue.TextAlignment.left if direction == DirectionType.rtl else VttCue.TextAlignment.right)
+
     self._paragraphs.append(cue)
 
     for elem in list(element):

src/test/python/test_vtt_writer.py

@@ -150,6 +150,60 @@ def test_position(self):
     vtt_from_model = vtt_writer.from_model(model, config)
     self.assertEqual(expected_vtt, vtt_from_model)
 
+  def test_align(self):
+    ttml_doc_str = """<?xml version="1.0" encoding="UTF-8"?>
+<tt xml:lang="en-US" xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xmlns:ttp="http://www.w3.org/ns/ttml#parameter" xmlns:ttm="http://www.w3.org/ns/ttml#metadata" ttp:frameRate="24" ttp:frameRateMultiplier="1000 1001" ttp:profile="http://www.w3.org/ns/ttml/profile/imsc1/text" ttp:timeBase="media">
+  <head>
+    <styling>
+      <style xml:id="style.center" tts:fontFamily="Arial" tts:fontSize="100%" tts:fontStyle="normal" tts:fontWeight="normal" tts:backgroundColor="transparent" tts:color="white" tts:textAlign="center"/>
+      <style xml:id="style.start" tts:fontFamily="Arial" tts:fontSize="100%" tts:fontStyle="normal" tts:fontWeight="normal" tts:backgroundColor="transparent" tts:color="white" tts:textAlign="start"/>
+      <style xml:id="style.end" tts:fontFamily="Arial" tts:fontSize="100%" tts:fontStyle="normal" tts:fontWeight="normal" tts:backgroundColor="transparent" tts:color="white" tts:textAlign="end"/>
+    </styling>
+    <layout>
+      <region xml:id="lr"                      tts:backgroundColor="transparent" tts:origin="10% 10%" tts:extent="80% 80%"/>
+      <region xml:id="rl" tts:writingMode="rl" tts:backgroundColor="transparent" tts:origin="10% 10%" tts:extent="80% 80%"/>
+    </layout>
+  </head>
+  <body>
+    <div>
+      <p style="style.center" region="lr" begin="00:00:03:12" end="00:00:12:00">Only one or two short samples are needed<br/>to make sure the conversion basically works</p>
+      <p style="style.start" region="lr" begin="00:00:14:09" end="00:00:25:17">Cool, got it, will do it by end of next week.</p>
+      <p style="style.end" region="lr" begin="00:00:26:00" end="00:00:28:00">Yes.</p>
+      <p style="style.end" region="rl" begin="00:00:29:00" end="00:00:31:00">Good.</p>
+    </div>
+  </body>
+</tt>"""
+
+    expected_vtt="""WEBVTT
+
+1
+00:00:03.501 --> 00:00:12.000 align:center
+Only one or two short samples are needed
+to make sure the conversion basically works
+
+2
+00:00:14.375 --> 00:00:25.709 align:left
+Cool, got it, will do it by end of next week.
+
+3
+00:00:26.000 --> 00:00:28.000 align:right
+Yes.
+
+4
+00:00:29.000 --> 00:00:31.000 align:left
+Good.
+"""
+
+    model = imsc_reader.to_model(et.ElementTree(et.fromstring(ttml_doc_str)))
+    config = VTTWriterConfiguration()
+    config.text_align = True
+    vtt_from_model = vtt_writer.from_model(model, config)
+    self.assertEqual(expected_vtt, vtt_from_model)
+
+    config = VTTWriterConfiguration.parse(json.loads('{"text_align":true}'))
+    vtt_from_model = vtt_writer.from_model(model, config)
+    self.assertEqual(expected_vtt, vtt_from_model)
+
   def test_cue_id(self):
     ttml_doc_str = """<?xml version="1.0" encoding="UTF-8"?>
 <tt xml:lang="en-US" xmlns="http://www.w3.org/ns/ttml" xmlns:ttp="http://www.w3.org/ns/ttml#parameter" ttp:frameRate="24" ttp:frameRateMultiplier="1000 1001">