Make Subtitle an abstract base class

av/codec/context.pyx

@@ -638,7 +638,7 @@ cdef class CodecContext:
     def skip_frame(self):
         """One of :class:`.SkipType`.
 
-        Wraps ffmpeg:`AVCodecContext.skip_frame`.
+        Wraps :ffmpeg:`AVCodecContext.skip_frame`.
 
         """
         return SkipType._get(self.ptr.skip_frame, create=True)

av/subtitles/stream.pyx

@@ -1,3 +1,6 @@
 cdef class SubtitleStream(Stream):
+    """
+    A :class:`SubtitleStream` can contain many :class:`SubtitleSet` objects accessible via decoding.
+    """
     def __getattr__(self, name):
         return getattr(self.codec_context, name)

av/subtitles/subtitle.pyi

@@ -11,8 +11,7 @@ class SubtitleSet:
     def __iter__(self) -> Iterator[Subtitle]: ...
     def __getitem__(self, i: int) -> Subtitle: ...
 
-class Subtitle:
-    type: Literal[b"none", b"bitmap", b"text", b"ass"]
+class Subtitle: ...
 
 class BitmapSubtitle(Subtitle):
     type: Literal[b"bitmap"]

av/subtitles/subtitle.pyx

@@ -11,6 +11,9 @@ cdef class SubtitleProxy:
 
 
 cdef class SubtitleSet:
+    """
+    A :class:`SubtitleSet` can contain many :class:`Subtitle` objects.
+    """
     def __cinit__(self, SubtitleProxy proxy):
         self.proxy = proxy
         cdef int i
@@ -50,9 +53,7 @@ cdef Subtitle build_subtitle(SubtitleSet subtitle, int index):
         raise ValueError("subtitle rect index out of range")
     cdef lib.AVSubtitleRect *ptr = subtitle.proxy.struct.rects[index]
 
-    if ptr.type == lib.SUBTITLE_NONE:
-        return Subtitle(subtitle, index)
-    elif ptr.type == lib.SUBTITLE_BITMAP:
+    if ptr.type == lib.SUBTITLE_BITMAP:
         return BitmapSubtitle(subtitle, index)
     elif ptr.type == lib.SUBTITLE_TEXT:
         return TextSubtitle(subtitle, index)
@@ -63,6 +64,10 @@ cdef Subtitle build_subtitle(SubtitleSet subtitle, int index):
 
 
 cdef class Subtitle:
+    """
+    An abstract base class for each concrete type of subtitle.
+    Wraps :ffmpeg:`AVSubtitleRect`
+    """
     def __cinit__(self, SubtitleSet subtitle, int index):
         if index < 0 or <unsigned int>index >= subtitle.proxy.struct.num_rects:
             raise ValueError("subtitle rect index out of range")