Fix WebVTT parsing when frame numbering is missing

As per <https://en.wikipedia.org/wiki/WebVTT>:

    The frame numbering/identification preceding
    the timecode is optional

manifest-chromium.json

@@ -17,5 +17,5 @@
     "activeTab",
     "<all_urls>"
   ],
-  "version": "1.0.0"
+  "version": "1.0.1"
 }

manifest-firefox.json

@@ -23,5 +23,5 @@
     "activeTab",
     "<all_urls>"
   ],
-  "version": "1.0.0"
+  "version": "1.0.1"
 }

src/assign-captions.js

@@ -104,20 +104,26 @@
         video.pause();
     };
 
+    // https://en.wikipedia.org/wiki/WebVTT#Main_differences_from_SubRip
+
     const srtParse = function(raw) {
         const vtt = [ 'WEBVTT', '' ];
         const entries = raw.replace(/(\r\n|\n\r)/g, '\n')
                            .trim()
                            .split(/\s*\n\n+\s*/);
         for ( const entry of entries ) {
+            let i = 0;
             const lines = entry.split(/\s*\n\s*/);
-            if ( /^\d+$/.test(lines[0]) === false ) { continue; }
-            const times = /(\S+)\s+--+>\s+(\S+)/.exec(lines[1]);
+            // "The frame numbering/identification preceding the
+            // "timecode is optional"
+            if ( /^\d+$/.test(lines[i+0]) ) {
+                i += 1;
+            }
+            const times = /^(\S+)\s+--+>\s+(\S+)/.exec(lines[i+0]);
             if ( times === null ) { continue; }
             vtt.push(
-                lines[0],
                 times[1].replace(/,/g, '.') + ' --> ' + times[2].replace(/,/g, '.'),
-                lines.slice(2).join('\n'),
+                lines.slice(i+1).join('\n'),
                 ''
             );
         }
@@ -136,7 +142,7 @@
         track.setAttribute('label', 'CCaptioner');
         track.setAttribute('srclang', 'zz');
         track.setAttribute('src', blobURL);
-        track.setAttribute('data-vtt-delta', '0');
+        track.setAttribute('data-vtt-offset', '0');
         track.setAttribute('data-vtt', vtt);
         video.appendChild(track);
         track.track.mode = 'showing';

src/offset-captions.js

@@ -53,19 +53,20 @@
 
     for ( let i = 0; i < entries.length; i++ ) {
         const lines = entries[i].split(/\n/);
-        const times = /(\S+) --> (\S+)/.exec(lines[1]);
+        const times = /(\S+) --> (\S+)/.exec(lines[0]);
         if ( times === null ) { continue; }
         const t0 = timeShift(times[1]);
         if ( t0 === '' ) { return; }
         const t1 = timeShift(times[2]);
-        lines[1] = `${t0} --> ${t1}`;
+        lines[0] = `${t0} --> ${t1}`;
         entries[i] = lines.join('\n');
     }
     vtt = entries.join('\n\n');
 
     const blob = new Blob([ vtt ], { type: 'text/vtt' });
     const blobURL = URL.createObjectURL(blob);
     const newTrack = oldTrack.cloneNode(false);
+    newTrack.setAttribute('data-vtt-offset', timeDelta);
     newTrack.setAttribute('src', blobURL);
     oldTrack.replaceWith(newTrack);
     newTrack.track.mode = 'showing';