fix(HLS): Support PATHWAY-ID (Content Steering) for subtitles (#9442)

Author: avelad

lib/hls/hls_parser.js

@@ -1478,20 +1478,31 @@ shaka.hls.HlsParser = class {
     // Create text stream for each Subtitle media tag.
     const subtitleTags =
         shaka.hls.Utils.filterTagsByType(mediaTags, 'SUBTITLES');
-    const textStreams = subtitleTags.map((tag) => {
-      const disableText = this.config_.disableText;
-      if (disableText) {
-        return null;
+
+    const groupedTags = {};
+    for (const tag of subtitleTags) {
+      const key = tag.getTagKey(!this.contentSteeringManager_);
+      if (!groupedTags[key]) {
+        groupedTags[key] = [tag];
+      } else {
+        groupedTags[key].push(tag);
       }
-      try {
-        return this.createStreamInfoFromMediaTags_([tag], new Map()).stream;
-      } catch (e) {
-        if (this.config_.hls.ignoreTextStreamFailures) {
-          return null;
+    }
+
+    const textStreams = [];
+    if (!this.config_.disableText) {
+      for (const key in groupedTags) {
+        try {
+          textStreams.push(this.createStreamInfoFromMediaTags_(
+              groupedTags[key], new Map()).stream);
+        } catch (e) {
+          if (this.config_.hls.ignoreTextStreamFailures) {
+            continue;
+          }
+          throw e;
         }
-        throw e;
       }
-    });
+    }
 
     const type = shaka.util.ManifestParserUtils.ContentType.TEXT;
 
@@ -2384,6 +2395,10 @@ shaka.hls.HlsParser = class {
       verbatimMediaPlaylistUris.push(uri);
       globalGroupIds.push(groupId);
       groupIdUriMapping.set(groupId, uri);
+      const pathwayId = tag.getAttributeValue('PATHWAY-ID');
+      if (pathwayId) {
+        groupIdPathwayIdMapping.set(groupId, pathwayId);
+      }
     }
 
     const globalGroupId = globalGroupIds.sort().join(',');

test/hls/hls_parser_unit.js

@@ -6210,15 +6210,19 @@ describe('HlsParser', () => {
       '#EXTM3U\n',
       '#EXT-X-CONTENT-STEERING:SERVER-URI="http://contentsteering",',
       'PATHWAY-ID="a"\n',
+      '#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subsA",LANGUAGE="eng",',
+      'NAME="English",PATHWAY-ID="a",URI="subs/a/media.m3u8"\n',
+      '#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subsB",LANGUAGE="eng",',
+      'NAME="English",PATHWAY-ID="b",URI="subs/b/media.m3u8"\n',
       '#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="a",LANGUAGE="eng",',
       'URI="audio/a/media.m3u8"\n',
       '#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="b",LANGUAGE="eng",',
       'URI="audio/b/media.m3u8"\n',
       '#EXT-X-STREAM-INF:BANDWIDTH=200,CODECS="avc,mp4a",',
-      'AUDIO="a",PATHWAY-ID="a",CLOSED-CAPTIONS=NONE\n',
+      'AUDIO="a",PATHWAY-ID="a",CLOSED-CAPTIONS=NONE,SUBTITLES="subsA"\n',
       'a/media.m3u8\n',
       '#EXT-X-STREAM-INF:BANDWIDTH=200,CODECS="avc,mp4a",',
-      'AUDIO="b",PATHWAY-ID="b",CLOSED-CAPTIONS=NONE\n',
+      'AUDIO="b",PATHWAY-ID="b",CLOSED-CAPTIONS=NONE,SUBTITLES="subsB"\n',
       'b/media.m3u8',
     ].join('');
 
@@ -6248,6 +6252,8 @@ describe('HlsParser', () => {
         .setResponseText('http://master/b/media.m3u8', media)
         .setResponseText('http://master/audio/a/media.m3u8', media)
         .setResponseText('http://master/audio/b/media.m3u8', media)
+        .setResponseText('http://master/subs/a/media.m3u8', media)
+        .setResponseText('http://master/subs/b/media.m3u8', media)
         .setMaxUris(2);
 
     /** @type {shaka.extern.Manifest} */
@@ -6273,6 +6279,17 @@ describe('HlsParser', () => {
 
     expect(videoUri0).toBe('http://master/b/main.mp4');
     expect(videoUri1).toBe('http://master/a/main.mp4');
+
+    expect(manifest.textStreams.length).toBe(1);
+    const text = manifest.textStreams[0];
+    await text.createSegmentIndex();
+    goog.asserts.assert(text.segmentIndex, 'Null segmentIndex!');
+    const textSegment0 = Array.from(text.segmentIndex)[0];
+    const textUri0 = textSegment0.getUris()[0];
+    const textUri1 = textSegment0.getUris()[1];
+
+    expect(textUri0).toBe('http://master/subs/b/main.mp4');
+    expect(textUri1).toBe('http://master/subs/a/main.mp4');
   });
 
   describe('EXT-X-DATERANGE', () => {