Loosley align live subtitle playlists and increase range of loaded su…

…bs to make up for playlist misalignment Resolves #3987
video-dev · Jun 3, 2021 · faf4472 · faf4472
1 parent 5e8468a
commit faf4472
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Showing 2 changed files with 19 additions and 14 deletions.
diff --git a/src/controller/level-helper.ts b/src/controller/level-helper.ts
@@ -372,17 +372,20 @@ export function adjustSliding(
   const delta =
     newDetails.startSN + newDetails.skippedSegments - oldDetails.startSN;
   const oldFragments = oldDetails.fragments;
-  const newFragments = newDetails.fragments;
   if (delta < 0 || delta >= oldFragments.length) {
     return;
   }
-  const playlistStartOffset = oldFragments[delta].start;
-  if (playlistStartOffset) {
-    for (let i = newDetails.skippedSegments; i < newFragments.length; i++) {
-      newFragments[i].start += playlistStartOffset;
+  addSliding(newDetails, oldFragments[delta].start);
+}
+
+export function addSliding(details: LevelDetails, start: number) {
+  if (start) {
+    const fragments = details.fragments;
+    for (let i = details.skippedSegments; i < fragments.length; i++) {
+      fragments[i].start += start;
     }
-    if (newDetails.fragmentHint) {
-      newDetails.fragmentHint.start += playlistStartOffset;
+    if (details.fragmentHint) {
+      details.fragmentHint.start += start;
     }
   }
 }

diff --git a/src/controller/subtitle-stream-controller.ts b/src/controller/subtitle-stream-controller.ts
@@ -3,7 +3,7 @@ import { logger } from '../utils/logger';
 import { BufferHelper } from '../utils/buffer-helper';
 import { findFragmentByPDT, findFragmentByPTS } from './fragment-finders';
 import { alignPDT } from '../utils/discontinuities';
-import { adjustSliding } from './level-helper';
+import { addSliding } from './level-helper';
 import { FragmentState } from './fragment-tracker';
 import BaseStreamController, { State } from './base-stream-controller';
 import { PlaylistLevelType } from '../types/loader';
@@ -250,9 +250,9 @@ export class SubtitleStreamController
         if (mainDetails) {
           if (newDetails.hasProgramDateTime && mainDetails.hasProgramDateTime) {
             alignPDT(newDetails, mainDetails);
-          } else {
-            // try aligning on SN
-            adjustSliding(mainDetails, newDetails);
+          } else if (mainDetails.fragments[0]) {
+            // line up live playlist with main so that fragments in range are loaded
+            addSliding(newDetails, mainDetails.fragments[0].start);
           }
         }
       } else {
@@ -321,21 +321,23 @@ export class SubtitleStreamController
         return;
       }
 
+      // Expand range of subs loaded by one target-duration in either direction to make up for misaligned playlists
+      const trackDetails = levels[currentTrackId].details as LevelDetails;
+      const targetDuration = trackDetails.targetduration;
       const { config, media } = this;
       const bufferedInfo = BufferHelper.bufferedInfo(
         this.mediaBufferTimeRanges,
-        media.currentTime,
+        media.currentTime - targetDuration,
         config.maxBufferHole
       );
       const { end: targetBufferTime, len: bufferLen } = bufferedInfo;
 
-      const maxBufLen = this.getMaxBufferLength();
+      const maxBufLen = this.getMaxBufferLength() + targetDuration;
 
       if (bufferLen > maxBufLen) {
         return;
       }
 
-      const trackDetails = levels[currentTrackId].details as LevelDetails;
       console.assert(
         trackDetails,
         'Subtitle track details are defined on idle subtitle stream controller tick'