fix(HLS): Fix subtitle timing

karma.conf.js

@@ -272,6 +272,8 @@ module.exports = (config) => {
       {pattern: 'test/test/assets/hls-raw-ec3/*', included: false},
       {pattern: 'test/test/assets/hls-raw-mp3/*', included: false},
       {pattern: 'test/test/assets/hls-sample-aes/*', included: false},
+      // eslint-disable-next-line max-len
+      {pattern: 'test/test/assets/hls-text-no-discontinuity/*', included: false},
       {pattern: 'test/test/assets/hls-text-offset/*', included: false},
       {pattern: 'test/test/assets/hls-ts-aac/*', included: false},
       {pattern: 'test/test/assets/hls-ts-ac3/*', included: false},

lib/hls/hls_parser.js

@@ -4126,7 +4126,7 @@ shaka.hls.HlsParser = class {
     let aesKey = undefined;
 
     let discontinuitySequence = shaka.hls.Utils.getFirstTagWithNameAsNumber(
-        playlist.tags, 'EXT-X-DISCONTINUITY-SEQUENCE', 0);
+        playlist.tags, 'EXT-X-DISCONTINUITY-SEQUENCE', -1);
     const mediaSequenceNumber = shaka.hls.Utils.getFirstTagWithNameAsNumber(
         playlist.tags, 'EXT-X-MEDIA-SEQUENCE', 0);
     const skipTag = shaka.hls.Utils.getFirstTagWithName(

lib/media/media_source_engine.js

@@ -1139,7 +1139,8 @@ shaka.media.MediaSourceEngine = class {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
 
     if (contentType == ContentType.TEXT) {
-      if (this.sequenceMode_) {
+      if (this.manifestType_ == shaka.media.ManifestParser.HLS &&
+          reference.discontinuitySequence >= 0) {
         // This won't be known until the first video segment is appended.
         const offset = await this.textSequenceModeOffset_;
         this.textEngine_.setTimestampOffset(offset);
@@ -1233,7 +1234,7 @@ shaka.media.MediaSourceEngine = class {
         const isBestSourceBufferForTimestamps =
             contentType == ContentType.VIDEO ||
             !(ContentType.VIDEO in this.sourceBuffers_);
-        if (this.sequenceMode_ && isBestSourceBufferForTimestamps) {
+        if (isBestSourceBufferForTimestamps) {
           this.textSequenceModeOffset_.resolve(timestampOffset);
         }
       }
@@ -1562,6 +1563,10 @@ shaka.media.MediaSourceEngine = class {
       this.textSequenceModeOffset_ = new shaka.util.PublicPromise();
     }
 
+    if (!this.sequenceMode_) {
+      return;
+    }
+
     // Queue an abort() to help MSE splice together overlapping segments.
     // We set appendWindowEnd when we change periods in DASH content, and the
     // period transition may result in overlap.

lib/media/segment_reference.js

@@ -295,7 +295,7 @@ shaka.media.SegmentReference = class {
     this.thumbnailSprite = null;
 
     /** @type {number} */
-    this.discontinuitySequence = 0;
+    this.discontinuitySequence = -1;
 
     /** @type {boolean} */
     this.allPartialSegments = allPartialSegments;

lib/media/streaming_engine.js

@@ -2152,17 +2152,15 @@ shaka.media.StreamingEngine = class {
       }
     }
 
-    if (this.manifest_.sequenceMode) {
-      const lastDiscontinuitySequence =
-          mediaState.lastSegmentReference ?
-              mediaState.lastSegmentReference.discontinuitySequence : null;
-      // Across discontinuity bounds, we should resync timestamps for
-      // sequence mode playbacks.  The next segment appended should
-      // land at its theoretical timestamp from the segment index.
-      if (reference.discontinuitySequence != lastDiscontinuitySequence) {
-        operations.push(this.playerInterface_.mediaSourceEngine.resync(
-            mediaState.type, reference.startTime));
-      }
+    const lastDiscontinuitySequence =
+        mediaState.lastSegmentReference ?
+            mediaState.lastSegmentReference.discontinuitySequence : null;
+    // Across discontinuity bounds, we should resync timestamps.  The next
+    // segment appended should land at its theoretical timestamp from the
+    // segment index.
+    if (reference.discontinuitySequence != lastDiscontinuitySequence) {
+      operations.push(this.playerInterface_.mediaSourceEngine.resync(
+          mediaState.type, reference.startTime));
     }
 
     await Promise.all(operations);

lib/text/vtt_text_parser.js

@@ -86,13 +86,7 @@ shaka.text.VttTextParser = class {
     // Only use 'X-TIMESTAMP-MAP' with HLS.  This overrides offset above.
     if (blocks[0].includes('X-TIMESTAMP-MAP') &&
         this.manifestType_ == shaka.media.ManifestParser.HLS) {
-      if (this.sequenceMode_) {
-        // Compute a different, rollover-based offset for sequence mode.
-        offset = this.computeHlsSequenceModeOffset_(blocks[0], time);
-      } else {
-        // Calculate the offset from the segment startTime.
-        offset = time.segmentStart;
-      }
+      offset = this.computeHlsOffset_(blocks[0], time);
     }
 
     // Parse VTT regions.
@@ -129,7 +123,7 @@ shaka.text.VttTextParser = class {
    * @return {number}
    * @private
    */
-  computeHlsSequenceModeOffset_(headerBlock, time) {
+  computeHlsOffset_(headerBlock, time) {
     // https://bit.ly/2K92l7y
     // The 'X-TIMESTAMP-MAP' header is used in HLS to align text with
     // the rest of the media.

test/hls/hls_parser_integration.js

@@ -111,10 +111,6 @@ describe('HlsParser', () => {
   });
 
   it('supports text discontinuity', async () => {
-    if (!shaka.util.Platform.supportsSequenceMode()) {
-      pending('Sequence mode is not supported by the platform.');
-    }
-
     player.setTextTrackVisibility(true);
 
     await player.load('/base/test/test/assets/hls-text-offset/index.m3u8');
@@ -134,4 +130,25 @@ describe('HlsParser', () => {
 
     await player.unload();
   });
+
+  it('supports text without discontinuity', async () => {
+    player.setTextTrackVisibility(true);
+
+    // eslint-disable-next-line max-len
+    await player.load('/base/test/test/assets/hls-text-no-discontinuity/index.m3u8');
+    await video.play();
+
+    await waiter.waitUntilPlayheadReachesOrFailOnTimeout(video, 1, 30);
+
+    const cues = video.textTracks[0].cues;
+    expect(cues.length).toBe(3);
+    expect(cues[0].startTime).toBeCloseTo(0.6, 0);
+    expect(cues[0].endTime).toBeCloseTo(2.88, 0);
+    expect(cues[1].startTime).toBeCloseTo(2.88, 0);
+    expect(cues[1].endTime).toBeCloseTo(6.36, 0);
+    expect(cues[2].startTime).toBeCloseTo(6.36, 0);
+    expect(cues[2].endTime).toBeCloseTo(10.68, 0);
+
+    await player.unload();
+  });
 });

test/hls/hls_parser_unit.js

@@ -1153,6 +1153,7 @@ describe('HlsParser', () => {
       '#EXT-X-VERSION:3\n',
       '#EXT-X-TARGETDURATION:5\n',
       '#EXT-X-MEDIA-SEQUENCE:0\n',
+      '#EXT-X-DISCONTINUITY-SEQUENCE:0\n',
       '#EXTINF:3,\n',
       'clip0-video-0.ts\n',
       '#EXTINF:1,\n',

test/test/assets/hls-text-no-discontinuity/av.m3u8

@@ -0,0 +1,11 @@
+#EXTM3U
+#EXT-X-VERSION:6
+#EXT-X-TARGETDURATION:7
+#EXT-X-MEDIA-SEQUENCE:0
+#EXT-X-PLAYLIST-TYPE:VOD
+#EXT-X-INDEPENDENT-SEGMENTS
+#EXTINF:6.000000,
+0.ts
+#EXTINF:6.000000,
+1.ts
+#EXT-X-ENDLIST

test/test/assets/hls-text-no-discontinuity/index.m3u8

@@ -0,0 +1,6 @@
+#EXTM3U
+#EXT-X-VERSION:6
+#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="de",DEFAULT=NO,AUTOSELECT=NO,LANGUAGE="de",FORCED="NO",URI="text.m3u8"
+
+#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1240800,CODECS="avc1.640014,mp4a.40.2",RESOLUTION=256x144,SUBTITLES="subs"
+av.m3u8

test/test/assets/hls-text-no-discontinuity/subtitle.vtt

@@ -0,0 +1,15 @@
+WEBVTT
+
+1
+00:00:00.600 --> 00:00:02.880
+Heute haben wir einen wesentlichen Meilenstein
+
+2
+00:00:02.880 --> 00:00:06.360
+auf dem Weg zur Science
+City Hamburg Bahrenfeld erreicht.
+
+3
+00:00:06.360 --> 00:00:10.680
+Die Science City ist ein 125 Hektar
+großes Areal in Bahrenfeld,

test/test/assets/hls-text-no-discontinuity/text.m3u8

@@ -0,0 +1,8 @@
+#EXTM3U
+#EXT-X-VERSION:3
+#EXT-X-PLAYLIST-TYPE:VOD
+#EXT-X-MEDIA-SEQUENCE:0
+#EXT-X-TARGETDURATION:12
+#EXTINF:12.000,
+subtitle.vtt
+#EXT-X-ENDLIST