[verified] Publish ReelBox source under GPLv3

2026-11-12 23:41:13 +00:00
commit db2b505ca3
@@ -0,0 +1,174 @@
+/// Converts already-decoded SRT, SSA/ASS or WebVTT text to plain-cue WebVTT.
+/// Deliberately drops styling, attachments, identifiers and positioning rather
+/// than allowing receiver-side fetches or pretending to preserve ASS rendering.
+class SubtitleWebVtt {
+  static String convert(String source) {
+    final text = source
+        .replaceFirst(RegExp(r'^\uFEFF'), '')
+        .replaceAll('\r\n', '\n')
+        .replaceAll('\r', '\n')
+        .trim();
+    final cues = <_Cue>[];
+    if (RegExp(r'^\[Script Info\]', caseSensitive: false).hasMatch(text)) {
+      _ass(text, cues);
+    } else {
+      final blocks = text.split(RegExp(r'\n[ \t]*\n'));
+      final vtt = RegExp(r'^WEBVTT(?:[ \t]|$)')
+          .hasMatch(blocks.first.split('\n').first);
+      if (vtt) blocks.removeAt(0); // Header metadata is never propagated.
+      for (final block in blocks) {
+        final lines = block.trim().split('\n');
+        if (vtt &&
+            RegExp(r'^(?:STYLE|REGION|NOTE)(?:[ \t]|$)')
+                .hasMatch(lines.first)) {
+          continue;
+        }
+        if (lines.length > 1 && !lines.first.contains('-->')) {
+          if (!vtt && !RegExp(r'^\d+$').hasMatch(lines.first)) {
+            throw const FormatException(
+              'Unsupported subtitle format; use SRT, SSA/ASS or WebVTT.',
+            );
+          }
+          lines.removeAt(0);
+        }
+        if (lines.length < 2) {
+          throw const FormatException('Invalid or empty subtitle cue.');
+        }
+        final timing = RegExp(r'^(\S+)[ \t]+-->[ \t]+(\S+)(?:[ \t]+.*)?$')
+            .firstMatch(lines.first);
+        if (timing == null) {
+          throw const FormatException(
+            'Unsupported subtitle format; use SRT, SSA/ASS or WebVTT.',
+          );
+        }
+        cues.add(
+          _Cue(
+            _time(timing[1]!, short: vtt),
+            _time(timing[2]!, short: vtt),
+            _plain(lines.skip(1).join('\n')),
+          ),
+        );
+      }
+    }
+    if (cues.isEmpty) {
+      throw const FormatException('No supported subtitle cues.');
+    }
+    var previous = -1;
+    for (final cue in cues) {
+      if (cue.end <= cue.start || cue.start < previous || cue.body.isEmpty) {
+        throw const FormatException(
+          'Invalid subtitle cue timing/order or empty text.',
+        );
+      }
+      previous = cue.start;
+    }
+    return 'WEBVTT\n\n${cues.map((c) => '${_stamp(c.start)} --> ${_stamp(c.end)}\n${c.body}').join('\n\n')}\n\n';
+  }
+
+  static int _time(String value, {bool short = false, bool ass = false}) {
+    final expression = ass
+        ? r'^(\d{1,6}):(\d{2}):(\d{2})\.(\d{2})$'
+        : r'^(\d{2,6}):(\d{2}):(\d{2})[.,](\d{3})$';
+    var match = RegExp(expression).firstMatch(value);
+    if (match == null && short) {
+      match = RegExp(r'^(\d{2}):(\d{2})\.(\d{3})$').firstMatch(value);
+      if (match != null) {
+        return _time('00:$value');
+      }
+    }
+    if (match == null) {
+      throw const FormatException('Invalid subtitle timestamp.');
+    }
+    final h = int.parse(match[1]!);
+    final m = int.parse(match[2]!);
+    final s = int.parse(match[3]!);
+    if (m > 59 || s > 59) {
+      throw const FormatException('Invalid subtitle timestamp range.');
+    }
+    return ((h * 60 + m) * 60 + s) * 1000 +
+        int.parse(match[4]!) * (ass ? 10 : 1);
+  }
+
+  static String _stamp(int ms) {
+    String pad(int value, int width) => '$value'.padLeft(width, '0');
+    return '${pad(ms ~/ 3600000, 2)}:${pad(ms ~/ 60000 % 60, 2)}:${pad(ms ~/ 1000 % 60, 2)}.${pad(ms % 1000, 3)}';
+  }
+
+  static void _ass(String text, List<_Cue> cues) {
+    var events = false;
+    List<String>? fields;
+    for (final raw in text.split('\n')) {
+      final line = raw.trim();
+      if (line.startsWith('[')) {
+        events = line.toLowerCase() == '[events]';
+        continue;
+      }
+      if (!events) continue;
+      if (line.toLowerCase().startsWith('format:')) {
+        fields = line
+            .substring(line.indexOf(':') + 1)
+            .split(',')
+            .map((s) => s.trim().toLowerCase())
+            .toList();
+      } else if (line.toLowerCase().startsWith('dialogue:')) {
+        if (fields == null ||
+            fields.last != 'text' ||
+            !fields.contains('start') ||
+            !fields.contains('end') ||
+            fields.toSet().length != fields.length) {
+          throw const FormatException('Invalid SSA/ASS Events format.');
+        }
+        final parts = line.substring(line.indexOf(':') + 1).split(',');
+        if (parts.length < fields.length) {
+          throw const FormatException('Incomplete SSA/ASS dialogue.');
+        }
+        final body = parts.skip(fields.length - 1).join(',');
+        if (RegExp(r'\\p[1-9]').hasMatch(body)) {
+          throw UnsupportedError('ASS drawing subtitles are not supported.');
+        }
+        cues.add(
+          _Cue(
+            _time(parts[fields.indexOf('start')].trim(), ass: true),
+            _time(parts[fields.indexOf('end')].trim(), ass: true),
+            _plain(
+              body
+                  .replaceAll(r'\N', '\n')
+                  .replaceAll(r'\n', '\n')
+                  .replaceAll(r'\h', ' '),
+            ),
+          ),
+        );
+      }
+    }
+  }
+
+  static String _plain(String body) {
+    // Plain escaped text is a strict subset of WebVTT: no HTML resources,
+    // CSS, voice/class attributes, ASS overrides, or embedded timing tags.
+    return body
+        .replaceAll(
+          RegExp(
+            r'<(script|style)\b[^>]*>.*?</\1\s*>',
+            caseSensitive: false,
+            dotAll: true,
+          ),
+          '',
+        )
+        .replaceAll(RegExp(r'\{[^}]*\}'), '')
+        .replaceAll(RegExp(r'<[^>]*>', dotAll: true), '')
+        .replaceAll(RegExp(r'[\x00-\x08\x0B\x0C\x0E-\x1F]'), '')
+        .replaceAll('&lt;', '<')
+        .replaceAll('&gt;', '>')
+        .replaceAll('&amp;', '&')
+        .replaceAll('&', '&amp;')
+        .replaceAll('<', '&lt;')
+        .replaceAll('>', '&gt;')
+        .trim();
+  }
+}
+
+class _Cue {
+  const _Cue(this.start, this.end, this.body);
+  final int start, end;
+  final String body;
+}