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-rw-r--r--yt_dlp/webvtt.py399
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diff --git a/yt_dlp/webvtt.py b/yt_dlp/webvtt.py
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+"""
+A partial parser for WebVTT segments. Interprets enough of the WebVTT stream
+to be able to assemble a single stand-alone subtitle file, suitably adjusting
+timestamps on the way, while everything else is passed through unmodified.
+
+Regular expressions based on the W3C WebVTT specification
+<https://www.w3.org/TR/webvtt1/>. The X-TIMESTAMP-MAP extension is described
+in RFC 8216 §3.5 <https://tools.ietf.org/html/rfc8216#section-3.5>.
+"""
+
+import io
+import re
+
+from .utils import int_or_none, timetuple_from_msec
+
+
+class _MatchParser:
+ """
+ An object that maintains the current parsing position and allows
+ conveniently advancing it as syntax elements are successfully parsed.
+ """
+
+ def __init__(self, string):
+ self._data = string
+ self._pos = 0
+
+ def match(self, r):
+ if isinstance(r, re.Pattern):
+ return r.match(self._data, self._pos)
+ if isinstance(r, str):
+ if self._data.startswith(r, self._pos):
+ return len(r)
+ return None
+ raise ValueError(r)
+
+ def advance(self, by):
+ if by is None:
+ amt = 0
+ elif isinstance(by, re.Match):
+ amt = len(by.group(0))
+ elif isinstance(by, str):
+ amt = len(by)
+ elif isinstance(by, int):
+ amt = by
+ else:
+ raise ValueError(by)
+ self._pos += amt
+ return by
+
+ def consume(self, r):
+ return self.advance(self.match(r))
+
+ def child(self):
+ return _MatchChildParser(self)
+
+
+class _MatchChildParser(_MatchParser):
+ """
+ A child parser state, which advances through the same data as
+ its parent, but has an independent position. This is useful when
+ advancing through syntax elements we might later want to backtrack
+ from.
+ """
+
+ def __init__(self, parent):
+ super().__init__(parent._data)
+ self.__parent = parent
+ self._pos = parent._pos
+
+ def commit(self):
+ """
+ Advance the parent state to the current position of this child state.
+ """
+ self.__parent._pos = self._pos
+ return self.__parent
+
+
+class ParseError(Exception):
+ def __init__(self, parser):
+ super().__init__("Parse error at position %u (near %r)" % (
+ parser._pos, parser._data[parser._pos:parser._pos + 100]
+ ))
+
+
+# While the specification <https://www.w3.org/TR/webvtt1/#webvtt-timestamp>
+# prescribes that hours must be *2 or more* digits, timestamps with a single
+# digit for the hour part has been seen in the wild.
+# See https://github.com/yt-dlp/yt-dlp/issues/921
+_REGEX_TS = re.compile(r'''(?x)
+ (?:([0-9]{1,}):)?
+ ([0-9]{2}):
+ ([0-9]{2})\.
+ ([0-9]{3})?
+''')
+_REGEX_EOF = re.compile(r'\Z')
+_REGEX_NL = re.compile(r'(?:\r\n|[\r\n]|$)')
+_REGEX_BLANK = re.compile(r'(?:\r\n|[\r\n])+')
+_REGEX_OPTIONAL_WHITESPACE = re.compile(r'[ \t]*')
+
+
+def _parse_ts(ts):
+ """
+ Convert a parsed WebVTT timestamp (a re.Match obtained from _REGEX_TS)
+ into an MPEG PES timestamp: a tick counter at 90 kHz resolution.
+ """
+ return 90 * sum(
+ int(part or 0) * mult for part, mult in zip(ts.groups(), (3600_000, 60_000, 1000, 1)))
+
+
+def _format_ts(ts):
+ """
+ Convert an MPEG PES timestamp into a WebVTT timestamp.
+ This will lose sub-millisecond precision.
+ """
+ return '%02u:%02u:%02u.%03u' % timetuple_from_msec(int((ts + 45) // 90))
+
+
+class Block:
+ """
+ An abstract WebVTT block.
+ """
+
+ def __init__(self, **kwargs):
+ for key, val in kwargs.items():
+ setattr(self, key, val)
+
+ @classmethod
+ def parse(cls, parser):
+ m = parser.match(cls._REGEX)
+ if not m:
+ return None
+ parser.advance(m)
+ return cls(raw=m.group(0))
+
+ def write_into(self, stream):
+ stream.write(self.raw)
+
+
+class HeaderBlock(Block):
+ """
+ A WebVTT block that may only appear in the header part of the file,
+ i.e. before any cue blocks.
+ """
+ pass
+
+
+class Magic(HeaderBlock):
+ _REGEX = re.compile(r'\ufeff?WEBVTT([ \t][^\r\n]*)?(?:\r\n|[\r\n])')
+
+ # XXX: The X-TIMESTAMP-MAP extension is described in RFC 8216 §3.5
+ # <https://tools.ietf.org/html/rfc8216#section-3.5>, but the RFC
+ # doesn’t specify the exact grammar nor where in the WebVTT
+ # syntax it should be placed; the below has been devised based
+ # on usage in the wild
+ #
+ # And strictly speaking, the presence of this extension violates
+ # the W3C WebVTT spec. Oh well.
+
+ _REGEX_TSMAP = re.compile(r'X-TIMESTAMP-MAP=')
+ _REGEX_TSMAP_LOCAL = re.compile(r'LOCAL:')
+ _REGEX_TSMAP_MPEGTS = re.compile(r'MPEGTS:([0-9]+)')
+ _REGEX_TSMAP_SEP = re.compile(r'[ \t]*,[ \t]*')
+
+ # This was removed from the spec in the 2017 revision;
+ # the last spec draft to describe this syntax element is
+ # <https://www.w3.org/TR/2015/WD-webvtt1-20151208/#webvtt-metadata-header>.
+ # Nevertheless, YouTube keeps serving those
+ _REGEX_META = re.compile(r'(?:(?!-->)[^\r\n])+:(?:(?!-->)[^\r\n])+(?:\r\n|[\r\n])')
+
+ @classmethod
+ def __parse_tsmap(cls, parser):
+ parser = parser.child()
+
+ while True:
+ m = parser.consume(cls._REGEX_TSMAP_LOCAL)
+ if m:
+ m = parser.consume(_REGEX_TS)
+ if m is None:
+ raise ParseError(parser)
+ local = _parse_ts(m)
+ if local is None:
+ raise ParseError(parser)
+ else:
+ m = parser.consume(cls._REGEX_TSMAP_MPEGTS)
+ if m:
+ mpegts = int_or_none(m.group(1))
+ if mpegts is None:
+ raise ParseError(parser)
+ else:
+ raise ParseError(parser)
+ if parser.consume(cls._REGEX_TSMAP_SEP):
+ continue
+ if parser.consume(_REGEX_NL):
+ break
+ raise ParseError(parser)
+
+ parser.commit()
+ return local, mpegts
+
+ @classmethod
+ def parse(cls, parser):
+ parser = parser.child()
+
+ m = parser.consume(cls._REGEX)
+ if not m:
+ raise ParseError(parser)
+
+ extra = m.group(1)
+ local, mpegts, meta = None, None, ''
+ while not parser.consume(_REGEX_NL):
+ if parser.consume(cls._REGEX_TSMAP):
+ local, mpegts = cls.__parse_tsmap(parser)
+ continue
+ m = parser.consume(cls._REGEX_META)
+ if m:
+ meta += m.group(0)
+ continue
+ raise ParseError(parser)
+ parser.commit()
+ return cls(extra=extra, mpegts=mpegts, local=local, meta=meta)
+
+ def write_into(self, stream):
+ stream.write('WEBVTT')
+ if self.extra is not None:
+ stream.write(self.extra)
+ stream.write('\n')
+ if self.local or self.mpegts:
+ stream.write('X-TIMESTAMP-MAP=LOCAL:')
+ stream.write(_format_ts(self.local if self.local is not None else 0))
+ stream.write(',MPEGTS:')
+ stream.write(str(self.mpegts if self.mpegts is not None else 0))
+ stream.write('\n')
+ if self.meta:
+ stream.write(self.meta)
+ stream.write('\n')
+
+
+class StyleBlock(HeaderBlock):
+ _REGEX = re.compile(r'''(?x)
+ STYLE[\ \t]*(?:\r\n|[\r\n])
+ ((?:(?!-->)[^\r\n])+(?:\r\n|[\r\n]))*
+ (?:\r\n|[\r\n])
+ ''')
+
+
+class RegionBlock(HeaderBlock):
+ _REGEX = re.compile(r'''(?x)
+ REGION[\ \t]*
+ ((?:(?!-->)[^\r\n])+(?:\r\n|[\r\n]))*
+ (?:\r\n|[\r\n])
+ ''')
+
+
+class CommentBlock(Block):
+ _REGEX = re.compile(r'''(?x)
+ NOTE(?:\r\n|[\ \t\r\n])
+ ((?:(?!-->)[^\r\n])+(?:\r\n|[\r\n]))*
+ (?:\r\n|[\r\n])
+ ''')
+
+
+class CueBlock(Block):
+ """
+ A cue block. The payload is not interpreted.
+ """
+
+ _REGEX_ID = re.compile(r'((?:(?!-->)[^\r\n])+)(?:\r\n|[\r\n])')
+ _REGEX_ARROW = re.compile(r'[ \t]+-->[ \t]+')
+ _REGEX_SETTINGS = re.compile(r'[ \t]+((?:(?!-->)[^\r\n])+)')
+ _REGEX_PAYLOAD = re.compile(r'[^\r\n]+(?:\r\n|[\r\n])?')
+
+ @classmethod
+ def parse(cls, parser):
+ parser = parser.child()
+
+ id = None
+ m = parser.consume(cls._REGEX_ID)
+ if m:
+ id = m.group(1)
+
+ m0 = parser.consume(_REGEX_TS)
+ if not m0:
+ return None
+ if not parser.consume(cls._REGEX_ARROW):
+ return None
+ m1 = parser.consume(_REGEX_TS)
+ if not m1:
+ return None
+ m2 = parser.consume(cls._REGEX_SETTINGS)
+ parser.consume(_REGEX_OPTIONAL_WHITESPACE)
+ if not parser.consume(_REGEX_NL):
+ return None
+
+ start = _parse_ts(m0)
+ end = _parse_ts(m1)
+ settings = m2.group(1) if m2 is not None else None
+
+ text = io.StringIO()
+ while True:
+ m = parser.consume(cls._REGEX_PAYLOAD)
+ if not m:
+ break
+ text.write(m.group(0))
+
+ parser.commit()
+ return cls(
+ id=id,
+ start=start, end=end, settings=settings,
+ text=text.getvalue()
+ )
+
+ def write_into(self, stream):
+ if self.id is not None:
+ stream.write(self.id)
+ stream.write('\n')
+ stream.write(_format_ts(self.start))
+ stream.write(' --> ')
+ stream.write(_format_ts(self.end))
+ if self.settings is not None:
+ stream.write(' ')
+ stream.write(self.settings)
+ stream.write('\n')
+ stream.write(self.text)
+ stream.write('\n')
+
+ @property
+ def as_json(self):
+ return {
+ 'id': self.id,
+ 'start': self.start,
+ 'end': self.end,
+ 'text': self.text,
+ 'settings': self.settings,
+ }
+
+ def __eq__(self, other):
+ return self.as_json == other.as_json
+
+ @classmethod
+ def from_json(cls, json):
+ return cls(
+ id=json['id'],
+ start=json['start'],
+ end=json['end'],
+ text=json['text'],
+ settings=json['settings']
+ )
+
+ def hinges(self, other):
+ if self.text != other.text:
+ return False
+ if self.settings != other.settings:
+ return False
+ return self.start <= self.end == other.start <= other.end
+
+
+def parse_fragment(frag_content):
+ """
+ A generator that yields (partially) parsed WebVTT blocks when given
+ a bytes object containing the raw contents of a WebVTT file.
+ """
+
+ parser = _MatchParser(frag_content.decode())
+
+ yield Magic.parse(parser)
+
+ while not parser.match(_REGEX_EOF):
+ if parser.consume(_REGEX_BLANK):
+ continue
+
+ block = RegionBlock.parse(parser)
+ if block:
+ yield block
+ continue
+ block = StyleBlock.parse(parser)
+ if block:
+ yield block
+ continue
+ block = CommentBlock.parse(parser)
+ if block:
+ yield block # XXX: or skip
+ continue
+
+ break
+
+ while not parser.match(_REGEX_EOF):
+ if parser.consume(_REGEX_BLANK):
+ continue
+
+ block = CommentBlock.parse(parser)
+ if block:
+ yield block # XXX: or skip
+ continue
+ block = CueBlock.parse(parser)
+ if block:
+ yield block
+ continue
+
+ raise ParseError(parser)