From fb1c90908d45820ee7c629ac4b6fc61235659165 Mon Sep 17 00:00:00 2001
From: Alex Barstow <alexander.barstow@gmail.com>
Date: Thu, 19 Nov 2020 14:59:54 -0500
Subject: [PATCH] fix: remove duplicate cues with same time interval and text
 (#1005)

---
 src/util/text-tracks.js   | 40 ++++++++++++++++++-
 src/vtt-segment-loader.js | 12 ++++--
 test/text-tracks.test.js  | 84 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 131 insertions(+), 5 deletions(-)

diff --git a/src/util/text-tracks.js b/src/util/text-tracks.js
index be57deecb..f130e7b1a 100644
--- a/src/util/text-tracks.js
+++ b/src/util/text-tracks.js
@@ -240,9 +240,47 @@ export const removeCuesFromTrack = function(start, end, track) {
   while (i--) {
     cue = track.cues[i];
 
-    // Remove any overlapping cue
+    // Remove any cue within the provided start and end time
     if (cue.startTime >= start && cue.endTime <= end) {
       track.removeCue(cue);
     }
   }
 };
+
+/**
+ * Remove duplicate cues from a track on video.js (a cue is considered a
+ * duplicate if it has the same time interval and text as another)
+ *
+ * @param {Object} track the text track to remove the duplicate cues from
+ * @private
+ */
+export const removeDuplicateCuesFromTrack = function(track) {
+  const cues = track.cues;
+
+  if (!cues) {
+    return;
+  }
+
+  for (let i = 0; i < cues.length; i++) {
+    const duplicates = [];
+    let occurrences = 0;
+
+    for (let j = 0; j < cues.length; j++) {
+      if (
+        cues[i].startTime === cues[j].startTime &&
+        cues[i].endTime === cues[j].endTime &&
+        cues[i].text === cues[j].text
+      ) {
+        occurrences++;
+
+        if (occurrences > 1) {
+          duplicates.push(cues[j]);
+        }
+      }
+    }
+
+    if (duplicates.length) {
+      duplicates.forEach(dupe => track.removeCue(dupe));
+    }
+  }
+};
diff --git a/src/vtt-segment-loader.js b/src/vtt-segment-loader.js
index 933b7805c..8edca0a57 100644
--- a/src/vtt-segment-loader.js
+++ b/src/vtt-segment-loader.js
@@ -4,7 +4,7 @@
 import SegmentLoader from './segment-loader';
 import videojs from 'video.js';
 import window from 'global/window';
-import { removeCuesFromTrack } from './util/text-tracks';
+import { removeCuesFromTrack, removeDuplicateCuesFromTrack } from './util/text-tracks';
 import { initSegmentId } from './bin-utils';
 import { uint8ToUtf8 } from './util/string';
 import { REQUEST_ERRORS } from './media-segment-request';
@@ -364,14 +364,20 @@ export default class VTTSegmentLoader extends SegmentLoader {
 
     this.mediaSecondsLoaded += segment.duration;
 
+    // Create VTTCue instances for each cue in the new segment and add them to
+    // the subtitle track
     segmentInfo.cues.forEach((cue) => {
-      // remove any overlapping cues to prevent doubling
-      this.remove(cue.startTime, cue.endTime);
       this.subtitlesTrack_.addCue(this.featuresNativeTextTracks_ ?
         new window.VTTCue(cue.startTime, cue.endTime, cue.text) :
         cue);
     });
 
+    // Remove any duplicate cues from the subtitle track. The WebVTT spec allows
+    // cues to have identical time-intervals, but if the text is also identical
+    // we can safely assume it is a duplicate that can be removed (ex. when a cue
+    // "overlaps" VTT segments)
+    removeDuplicateCuesFromTrack(this.subtitlesTrack_);
+
     this.handleAppendsDone_();
   }
 
diff --git a/test/text-tracks.test.js b/test/text-tracks.test.js
index 1500db70a..97ab0cbc2 100644
--- a/test/text-tracks.test.js
+++ b/test/text-tracks.test.js
@@ -4,7 +4,8 @@ import {
   createCaptionsTrackIfNotExists,
   addCaptionData,
   createMetadataTrackIfNotExists,
-  addMetadata
+  addMetadata,
+  removeDuplicateCuesFromTrack
 } from '../src/util/text-tracks';
 
 const { module, test } = Qunit;
@@ -16,6 +17,11 @@ class MockTextTrack {
   addCue(cue) {
     this.cues.push(cue);
   }
+  removeCue(cue) {
+    const cueIndex = this.cues.map(c => c.text).indexOf(cue.text);
+
+    this.cues.splice(cueIndex, 1);
+  }
 }
 
 class MockTech {
@@ -302,3 +308,79 @@ test('adds cues for each metadata frame seen', function(assert) {
     'ended at duration 20'
   );
 });
+
+test('removeDuplicateCuesFromTrack removes all but one cue with identical startTime, endTime, and text', function(assert) {
+  const track = new MockTextTrack();
+
+  [{
+    startTime: 0,
+    endTime: 1,
+    text: 'CC1 text'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Identical'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Identical'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Identical'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Identical'
+  }, {
+    startTime: 2,
+    endTime: 3,
+    text: 'CC3 text'
+  }].forEach((mockCue) => {
+    track.addCue(mockCue);
+  });
+
+  assert.equal(track.cues.length, 6, '6 cues present initially');
+
+  removeDuplicateCuesFromTrack(track);
+
+  assert.equal(track.cues.length, 3, '3 cue remains after duplicates removed');
+});
+
+test('removeDuplicateCuesFromTrack leaves in cues with the same startTime and endTime, but different text-- or vice-versa', function(assert) {
+  const track = new MockTextTrack();
+
+  [{
+    startTime: 0,
+    endTime: 1,
+    text: 'Identical'
+  }, {
+    startTime: 0,
+    endTime: 1,
+    text: 'Identical'
+  }, {
+    startTime: 0,
+    endTime: 1,
+    text: 'CC2 text'
+  }, {
+    startTime: 0,
+    endTime: 1,
+    text: 'CC3 text'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Also identical'
+  }, {
+    startTime: 1,
+    endTime: 2,
+    text: 'Also identical'
+  }].forEach((mockCue) => {
+    track.addCue(mockCue);
+  });
+
+  assert.equal(track.cues.length, 6, '6 cues present initially');
+
+  removeDuplicateCuesFromTrack(track);
+
+  assert.equal(track.cues.length, 4, '4 cues remain after duplicates removed');
+});