Pr for media sequence

src/sync-controller.js

@@ -6,6 +6,10 @@ 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.
+const MAX_MEDIA_SEQUENCE_DIFF_FOR_SYNC = 1000;
+
 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 +368,12 @@ 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 = 2000;
+
+ 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);