Pr for media sequence

src/sync-controller.js

@@ -6,6 +6,13 @@ import {sumDurations, getPartsAndSegments} from './playlist';
 import videojs from 'video.js';
 import logger from './util/logger';
 
+// The maximum gap allowed between two media sequence tags when trying to
+// synchronize expired playlist segments.
+// the max media sequence diff is 48 hours of live stream
+// content with two second segments. Anything larger than that
+// will likely be invalid.
+const MAX_MEDIA_SEQUENCE_DIFF_FOR_SYNC = 86400;
+
 export const syncPointStrategies = [
   // Stategy "VOD": Handle the VOD-case where the sync-point is *always*
   //                the equivalence display-time 0 === segment-index 0
@@ -364,6 +371,12 @@ export default class SyncController extends videojs.EventTarget {
   saveExpiredSegmentInfo(oldPlaylist, newPlaylist) {
     const mediaSequenceDiff = newPlaylist.mediaSequence - oldPlaylist.mediaSequence;
 
+    // Ignore large media sequence gaps
+    if (mediaSequenceDiff > MAX_MEDIA_SEQUENCE_DIFF_FOR_SYNC) {
+      videojs.log.warn(`Not saving expired segment info. Media sequence gap ${mediaSequenceDiff} is too large.`);
+      return;
+    }
+
     // When a segment expires from the playlist and it has a start time
     // save that information as a possible sync-point reference in future
     for (let i = mediaSequenceDiff - 1; i >= 0; i--) {

test/sync-controller.test.js

@@ -441,6 +441,24 @@ QUnit.test('saves expired info onto new playlist for sync point', function(asser
   );
 });
 
+QUnit.test('skips save of expired segment info if media sequence gap too large', function(assert) {
+  const oldPlaylist = playlistWithDuration(50);
+  const newPlaylist = playlistWithDuration(50);
+
+  oldPlaylist.mediaSequence = 100;
+  newPlaylist.mediaSequence = 86501;
+
+  oldPlaylist.segments[0].start = 390;
+  oldPlaylist.segments[1].start = 400;
+
+  this.syncController.saveExpiredSegmentInfo(oldPlaylist, newPlaylist);
+
+  assert.strictEqual(
+    typeof newPlaylist.syncInfo, 'undefined',
+    'skipped saving sync info onto new playlist'
+  );
+});
+
 QUnit.test('saves segment timing info', function(assert) {
   const syncCon = this.syncController;
   const playlist = playlistWithDuration(60);