Re-align audio playlist with main when there is no overlap between au…

…dio playlist updates (#6857)

* Attempt to realign audio with main when `alignPlaylists` finds no overlap in playlist updates
#6823
* Cache audio playlist responses until main playlist is alignable
* Align on starting discontinuity tag with discontinuity-sequence (startCC is discontinuity-sequence)

src/controller/audio-stream-controller.ts

@@ -9,7 +9,10 @@ import { ElementaryStreamTypes, isMediaFragment } from '../loader/fragment';
 import { Level } from '../types/level';
 import { PlaylistContextType, PlaylistLevelType } from '../types/loader';
 import { ChunkMetadata } from '../types/transmuxer';
-import { alignMediaPlaylistByPDT } from '../utils/discontinuities';
+import {
+  alignDiscontinuities,
+  alignMediaPlaylistByPDT,
+} from '../utils/discontinuities';
 import { mediaAttributesIdentical } from '../utils/media-option-attributes';
 import type { FragmentTracker } from './fragment-tracker';
 import type Hls from '../hls';
@@ -257,7 +260,7 @@ class AudioStreamController
             this.nextLoadPosition = this.findSyncFrag(videoAnchor).start;
             this.clearWaitingFragment();
           }
-        } else if (this.state !== State.STOPPED) {
+        } else {
           this.state = State.IDLE;
         }
       }
@@ -508,22 +511,30 @@ class AudioStreamController
 
   private onLevelLoaded(event: Events.LEVEL_LOADED, data: LevelLoadedData) {
     this.mainDetails = data.details;
-    if (this.cachedTrackLoadedData !== null) {
-      this.hls.trigger(Events.AUDIO_TRACK_LOADED, this.cachedTrackLoadedData);
+    const cachedTrackLoadedData = this.cachedTrackLoadedData;
+    if (cachedTrackLoadedData) {
       this.cachedTrackLoadedData = null;
+      this.hls.trigger(Events.AUDIO_TRACK_LOADED, cachedTrackLoadedData);
     }
   }
 
   private onAudioTrackLoaded(
     event: Events.AUDIO_TRACK_LOADED,
     data: TrackLoadedData,
   ) {
-    if (this.mainDetails == null) {
+    const { levels } = this;
+    const { details: newDetails, id: trackId } = data;
+    if (
+      this.mainDetails == null ||
+      this.mainDetails.expired ||
+      newDetails.endCC > this.mainDetails.endCC
+    ) {
       this.cachedTrackLoadedData = data;
+      if (this.state !== State.STOPPED) {
+        this.state = State.WAITING_TRACK;
+      }
       return;
     }
-    const { levels } = this;
-    const { details: newDetails, id: trackId } = data;
     if (!levels) {
       this.warn(`Audio tracks were reset while loading level ${trackId}`);
       return;
@@ -546,22 +557,23 @@ class AudioStreamController
       if (newDetails.deltaUpdateFailed || !mainDetails) {
         return;
       }
-      if (
-        !track.details &&
-        newDetails.hasProgramDateTime &&
-        mainDetails.hasProgramDateTime
-      ) {
-        // Make sure our audio rendition is aligned with the "main" rendition, using
-        // pdt as our reference times.
-        alignMediaPlaylistByPDT(newDetails, mainDetails);
-        sliding = newDetails.fragmentStart;
-      } else {
+
+      if (track.details) {
         sliding = this.alignPlaylists(
           newDetails,
           track.details,
           this.levelLastLoaded?.details,
         );
       }
+      if (!newDetails.alignedSliding) {
+        // Align audio rendition with the "main" playlist on discontinuity change
+        // or program-date-time (PDT)
+        alignDiscontinuities(newDetails, mainDetails);
+        if (!newDetails.alignedSliding) {
+          alignMediaPlaylistByPDT(newDetails, mainDetails);
+        }
+        sliding = newDetails.fragmentStart;
+      }
     }
     track.details = newDetails;
     this.levelLastLoaded = track;
@@ -665,7 +677,9 @@ class AudioStreamController
         complete: false,
       });
       cache.push(new Uint8Array(payload));
-      this.state = State.WAITING_INIT_PTS;
+      if (this.state !== State.STOPPED) {
+        this.state = State.WAITING_INIT_PTS;
+      }
     }
   }
 

src/controller/base-stream-controller.ts

@@ -1593,15 +1593,12 @@ export default class BaseStreamController
     const firstLevelLoad = !previousDetails;
     const aligned = details.alignedSliding && Number.isFinite(slidingStart);
     if (firstLevelLoad || (!aligned && !slidingStart)) {
-      const { fragPrevious } = this;
-      alignStream(fragPrevious, switchDetails, details);
+      alignStream(switchDetails, details);
       const alignedSlidingStart = details.fragmentStart;
       this.log(
         `Live playlist sliding: ${alignedSlidingStart.toFixed(2)} start-sn: ${
           previousDetails ? previousDetails.startSN : 'na'
-        }->${details.startSN} prev-sn: ${
-          fragPrevious ? fragPrevious.sn : 'na'
-        } fragments: ${length}`,
+        }->${details.startSN} fragments: ${length}`,
       );
       return alignedSlidingStart;
     }

src/loader/m3u8-parser.ts

@@ -526,7 +526,7 @@ export default class M3U8Parser {
           }
 
           case 'DISCONTINUITY-SEQUENCE':
-            discontinuityCounter = parseInt(value1);
+            level.startCC = discontinuityCounter = parseInt(value1);
             break;
           case 'KEY': {
             const levelKey = parseKey(value1, baseurl, level);
@@ -671,7 +671,7 @@ export default class M3U8Parser {
       if (!level.live) {
         lastFragment.endList = true;
       }
-      if (firstFragment) {
+      if (firstFragment && !level.startCC) {
         level.startCC = firstFragment.cc;
       }
       /**

src/utils/discontinuities.ts

@@ -57,12 +57,10 @@ export function adjustSlidingStart(sliding: number, details: LevelDetails) {
  * The PTS of a fragment lets Hls.js know where it fits into a stream - by knowing every PTS, we know which fragment to
  * download at any given time. PTS is normally computed when the fragment is demuxed, so taking this step saves us time
  * and an extra download.
- * @param lastFrag
  * @param lastLevel
  * @param details
  */
 export function alignStream(
-  lastFrag: Fragment | null,
   switchDetails: LevelDetails | undefined,
   details: LevelDetails,
 ) {

src/utils/level-helper.ts

@@ -229,7 +229,9 @@ export function mergeDetails(
         newDetails.fragments.shift();
       }
       newDetails.startSN = newDetails.fragments[0].sn;
-      newDetails.startCC = newDetails.fragments[0].cc;
+      if (!newDetails.startCC) {
+        newDetails.startCC = newDetails.fragments[0].cc;
+      }
     } else {
       if (newDetails.canSkipDateRanges) {
         newDetails.dateRanges = mergeDateRanges(