Fix subtitle segment loading hanging on live start with mismatched discontinuity

robwalch · robwalch · commit 775240248ed5 · 2025-06-26T09:39:57.000-07:00
Fixes #7347
diff --git a/src/controller/subtitle-stream-controller.ts b/src/controller/subtitle-stream-controller.ts
@@ -129,10 +129,12 @@ export class SubtitleStreamController
     data: SubtitleFragProcessed,
   ) {
     const { frag, success } = data;
-    if (isMediaFragment(frag)) {
-      this.fragPrevious = frag;
+    if (!this.fragContextChanged(frag)) {
+      if (isMediaFragment(frag)) {
+        this.fragPrevious = frag;
+      }
+      this.state = State.IDLE;
     }
-    this.state = State.IDLE;
     if (!success) {
       return;
     }
@@ -295,8 +297,12 @@ export class SubtitleStreamController
     this.mediaBuffer = this.mediaBufferTimeRanges;
     let sliding = 0;
     if (newDetails.live || track.details?.live) {
+      if (newDetails.deltaUpdateFailed) {
+        return;
+      }
       const mainDetails = this.mainDetails;
-      if (newDetails.deltaUpdateFailed || !mainDetails) {
+      if (!mainDetails) {
+        this.startFragRequested = false;
         return;
       }
       const mainSlidingStartFragment = mainDetails.fragments[0];
@@ -321,6 +327,10 @@ export class SubtitleStreamController
           addSliding(newDetails, sliding);
         }
       }
+      // compute start position if we are aligned with the main playlist
+      if (mainDetails && !this.startFragRequested) {
+        this.setStartPosition(mainDetails, sliding);
+      }
     }
     track.details = newDetails;
     this.levelLastLoaded = track;
diff --git a/src/controller/timeline-controller.ts b/src/controller/timeline-controller.ts
@@ -202,8 +202,18 @@ export class TimelineController implements ComponentAPI {
     // Parse any unparsed fragments upon receiving the initial PTS.
     if (unparsedVttFrags.length) {
       this.unparsedVttFrags = [];
-      unparsedVttFrags.forEach((frag) => {
-        this.onFragLoaded(Events.FRAG_LOADED, frag as FragLoadedData);
+      unparsedVttFrags.forEach((data) => {
+        if (this.initPTS[data.frag.cc]) {
+          this.onFragLoaded(Events.FRAG_LOADED, data as FragLoadedData);
+        } else {
+          this.hls.trigger(Events.SUBTITLE_FRAG_PROCESSED, {
+            success: false,
+            frag: data.frag,
+            error: new Error(
+              'Subtitle discontinuity domain does not match main',
+            ),
+          });
+        }
       });
     }
   }
diff --git a/tests/unit/controller/subtitle-stream-controller.ts b/tests/unit/controller/subtitle-stream-controller.ts
@@ -1,14 +1,18 @@
+import chai from 'chai';
 import sinon from 'sinon';
-
-import Hls from '../../../src/hls';
-import { Events } from '../../../src/events';
+import sinonChai from 'sinon-chai';
+import { State } from '../../../src/controller/base-stream-controller';
 import { FragmentTracker } from '../../../src/controller/fragment-tracker';
+import { SubtitleStreamController } from '../../../src/controller/subtitle-stream-controller';
+import { Events } from '../../../src/events';
+import Hls from '../../../src/hls';
 import { Fragment } from '../../../src/loader/fragment';
+import KeyLoader from '../../../src/loader/key-loader';
 import { PlaylistLevelType } from '../../../src/types/loader';
 import { AttrList } from '../../../src/utils/attr-list';
-import KeyLoader from '../../../src/loader/key-loader';
-import { State } from '../../../src/controller/base-stream-controller';
-import { SubtitleStreamController } from '../../../src/controller/subtitle-stream-controller';
+
+chai.use(sinonChai);
+const expect = chai.expect;
 
 const mediaMock = {
   currentTime: 0,
@@ -20,11 +24,11 @@ const tracksMock = [
   {
     id: 0,
     details: { url: '', fragments: [] },
-    attrs: new AttrList(),
+    attrs: new AttrList({}),
   },
   {
     id: 1,
-    attrs: new AttrList(),
+    attrs: new AttrList({}),
   },
 ];
 
@@ -38,7 +42,7 @@ describe('SubtitleStreamController', function () {
     hls = new Hls({});
     mediaMock.currentTime = 0;
     fragmentTracker = new FragmentTracker(hls);
-    keyLoader = new KeyLoader({});
+    keyLoader = new KeyLoader(hls.config);
 
     subtitleStreamController = new SubtitleStreamController(
       hls,
diff --git a/tests/unit/controller/timeline-controller.ts b/tests/unit/controller/timeline-controller.ts
@@ -1,6 +1,11 @@
+import chai from 'chai';
+import sinonChai from 'sinon-chai';
 import { TimelineController } from '../../../src/controller/timeline-controller';
-import Hls from '../../../src/hls';
 import { Events } from '../../../src/events';
+import Hls from '../../../src/hls';
+
+chai.use(sinonChai);
+const expect = chai.expect;
 
 describe('TimelineController', function () {
   let timelineController;
