fix(TTML): Fix duplicate cues overlapping segment boundaries (shaka-p…

…roject#4798)

Closes shaka-project#4631

lib/text/ttml_text_parser.js

@@ -136,7 +136,7 @@ shaka.text.TtmlTextParser = class {
     }
 
     const cue = TtmlTextParser.parseCue_(
-        body, time.periodStart, rateInfo, metadataElements, styles,
+        body, time, rateInfo, metadataElements, styles,
         regionElements, cueRegions, whitespaceTrim,
         cellResolutionInfo, /* parentCueElement= */ null,
         /* isContent= */ false);
@@ -157,7 +157,7 @@ shaka.text.TtmlTextParser = class {
    * Parses a TTML node into a Cue.
    *
    * @param {!Node} cueNode
-   * @param {number} offset
+   * @param {shaka.extern.TextParser.TimeContext} timeContext
    * @param {!shaka.text.TtmlTextParser.RateInfo_} rateInfo
    * @param {!Array.<!Element>} metadataElements
    * @param {!Array.<!Element>} styles
@@ -171,7 +171,7 @@ shaka.text.TtmlTextParser = class {
    * @private
    */
   static parseCue_(
-      cueNode, offset, rateInfo, metadataElements, styles, regionElements,
+      cueNode, timeContext, rateInfo, metadataElements, styles, regionElements,
       cueRegions, whitespaceTrim, cellResolution, parentCueElement, isContent) {
     /** @type {Element} */
     let cueElement;
@@ -236,7 +236,7 @@ shaka.text.TtmlTextParser = class {
       for (const childNode of cueElement.childNodes) {
         const nestedCue = shaka.text.TtmlTextParser.parseCue_(
             childNode,
-            offset,
+            timeContext,
             rateInfo,
             metadataElements,
             styles,
@@ -293,15 +293,20 @@ shaka.text.TtmlTextParser = class {
     if (start == null) {
       start = 0;
     }
-    start += offset;
+    start += timeContext.periodStart;
 
     // If end is null, that means the duration is effectively infinite.
     if (end == null) {
       end = Infinity;
     } else {
-      end += offset;
+      end += timeContext.periodStart;
     }
 
+    // Clip times to segment boundaries.
+    // https://github.com/shaka-project/shaka-player/issues/4631
+    start = Math.max(start, timeContext.segmentStart);
+    end = Math.min(end, timeContext.segmentEnd);
+
     if (!hasTimeAttributes && nestedCues.length > 0) {
       // If no time is defined for this cue, base the timing information on
       // the time of the nested cues. In the case of multiple nested cues with

test/text/mp4_ttml_parser_unit.js

@@ -41,7 +41,8 @@ describe('Mp4TtmlParser', () => {
   it('handles media segments with multiple mdats', () => {
     const parser = new shaka.text.Mp4TtmlParser();
     parser.parseInit(ttmlInitSegment);
-    const time = {periodStart: 0, segmentStart: 0, segmentEnd: 0, vttOffset: 0};
+    const time =
+        {periodStart: 0, segmentStart: 0, segmentEnd: 60, vttOffset: 0};
     const ret = parser.parseMedia(ttmlSegmentMultipleMDAT, time);
     // Bodies.
     expect(ret.length).toBe(2);
@@ -55,9 +56,9 @@ describe('Mp4TtmlParser', () => {
 
   it('accounts for offset', () => {
     const time1 =
-        {periodStart: 0, segmentStart: 0, segmentEnd: 0, vttOffset: 0};
+        {periodStart: 0, segmentStart: 0, segmentEnd: 70, vttOffset: 0};
     const time2 =
-        {periodStart: 7, segmentStart: 0, segmentEnd: 0, vttOffset: 7};
+        {periodStart: 7, segmentStart: 0, segmentEnd: 70, vttOffset: 7};
 
     const parser = new shaka.text.Mp4TtmlParser();
     parser.parseInit(ttmlInitSegment);
@@ -161,7 +162,8 @@ describe('Mp4TtmlParser', () => {
     ];
     const parser = new shaka.text.Mp4TtmlParser();
     parser.parseInit(ttmlInitSegment);
-    const time = {periodStart: 0, segmentStart: 0, segmentEnd: 0, vttOffset: 0};
+    const time =
+        {periodStart: 0, segmentStart: 0, segmentEnd: 60, vttOffset: 0};
     const result = parser.parseMedia(ttmlSegment, time);
     shaka.test.TtmlUtils.verifyHelper(
         cues, result, {startTime: 23, endTime: 53.5});