feat: Add support for forced subtitles (#208)

streamer/autodetect.py

@@ -173,3 +173,13 @@ def get_channel_layout(input: Input) -> Optional[AudioChannelLayoutName]:
       return bucket.get_key()
 
   return None
+
+def get_forced_subttitle(input: Input) -> bool:
+  """Returns the forced subtitle value of the input."""
+
+  forced_subttitle_string = _probe(input, 'disposition=forced')
+
+  if forced_subttitle_string is None:
+    return False
+
+  return bool(forced_subttitle_string)

streamer/input_configuration.py

@@ -211,6 +211,12 @@ class Input(configuration.Base):
   Not supported with media_type of 'text'.
   """
 
+  forced_subtitle = configuration.Field(bool).cast()
+  """Indicates that the subtitle is forced.
+
+  Only supported with media_type of 'text'.
+  """
+
 
   def __init__(self, *args) -> None:
     super().__init__(*args)
@@ -264,6 +270,8 @@ def disallow_field(name: str, reason: str) -> None:
         reason = 'text streams are not supported in input_type "{}"'.format(
             self.input_type.value)
         disallow_field('input_type', reason)
+      if self.forced_subtitle is None:
+        self.forced_subtitle = autodetect.get_forced_subttitle(self)
 
       # These fields are not supported with text, because we don't process or
       # transcode it.

streamer/packager_node.py

@@ -144,6 +144,9 @@ def _setup_stream(self, stream: OutputStream) -> str:
     if stream.input.drm_label:
       dict['drm_label'] = stream.input.drm_label
 
+    if stream.input.forced_subtitle:
+      dict['forced_subtitle'] = '1'
+
     # Note: Shaka Packager will not accept 'und' as a language, but Shaka
     # Player will fill that in if the language metadata is missing from the
     # manifest/playlist.

tests/tests.js

@@ -1066,6 +1066,7 @@ function textTracksTests(manifestUrl, format) {
           'name': TEST_DIR + 'Sintel.2010.Arabic.vtt',
           'media_type': 'text',
           'language': 'ar',
+          'forced_subtitle': true,
         },
       ],
     };
@@ -1084,6 +1085,8 @@ function textTracksTests(manifestUrl, format) {
     const languageList = trackList.map(track => track.language);
     languageList.sort();
     expect(languageList).toEqual(['ar', 'en', 'eo', 'es']);
+    const arTrack = trackList.find(track => track.language == 'ar');
+    expect(arTrack.forced).toBeTruthy();
   });
 }