Only allow large gaps to be skipped if start gap or all fragments in …

…range are partial (#5366)

* Only allow large gaps to be skipped if start gap or all fragments in range are partial
Fixes #5360

* Fix adaptation and fragment tracking after fragment errors (gap tags)
#2940

api-extractor/report/hls.js.api.md

@@ -278,7 +278,7 @@ export class BaseSegment {
 //
 // @public (undocumented)
 export class BaseStreamController extends TaskLoop implements NetworkComponentAPI {
-    constructor(hls: Hls, fragmentTracker: FragmentTracker, keyLoader: KeyLoader, logPrefix: string);
+    constructor(hls: Hls, fragmentTracker: FragmentTracker, keyLoader: KeyLoader, logPrefix: string, playlistType: PlaylistLevelType);
     // (undocumented)
     protected afterBufferFlushed(media: Bufferable, bufferType: SourceBufferName, playlistType: PlaylistLevelType): void;
     // (undocumented)
@@ -412,12 +412,16 @@ export class BaseStreamController extends TaskLoop implements NetworkComponentAP
     // (undocumented)
     protected onvseeking: EventListener | null;
     // (undocumented)
+    protected playlistType: PlaylistLevelType;
+    // (undocumented)
     protected recoverWorkerError(data: ErrorData): void;
     // (undocumented)
     protected reduceLengthAndFlushBuffer(data: ErrorData): boolean;
     // (undocumented)
     protected reduceMaxBufferLength(threshold: number): boolean;
     // (undocumented)
+    protected removeUnbufferedFrags(start?: number): void;
+    // (undocumented)
     protected resetFragmentErrors(filterType: PlaylistLevelType): void;
     // (undocumented)
     protected resetFragmentLoading(frag: Fragment): void;
@@ -428,6 +432,8 @@ export class BaseStreamController extends TaskLoop implements NetworkComponentAP
     // (undocumented)
     protected resetTransmuxer(): void;
     // (undocumented)
+    protected resetWhenMissingContext(chunkMeta: ChunkMetadata): void;
+    // (undocumented)
     protected retryDate: number;
     // (undocumented)
     protected seekToStartPos(): void;

src/controller/abr-controller.ts

@@ -357,8 +357,14 @@ class AbrController implements AbrComponentAPI {
     // compute next level using ABR logic
     let nextABRAutoLevel = this.getNextABRAutoLevel();
     // use forced auto level when ABR selected level has errored
-    if (forcedAutoLevel !== -1 && this.hls.levels[nextABRAutoLevel].loadError) {
-      return forcedAutoLevel;
+    if (forcedAutoLevel !== -1) {
+      const levels = this.hls.levels;
+      if (
+        levels.length > Math.max(forcedAutoLevel, nextABRAutoLevel) &&
+        levels[forcedAutoLevel].loadError <= levels[nextABRAutoLevel].loadError
+      ) {
+        return forcedAutoLevel;
+      }
     }
     // if forced auto level has been defined, use it to cap ABR computed quality level
     if (forcedAutoLevel !== -1) {

src/controller/audio-stream-controller.ts

@@ -64,7 +64,13 @@ class AudioStreamController
     fragmentTracker: FragmentTracker,
     keyLoader: KeyLoader
   ) {
-    super(hls, fragmentTracker, keyLoader, '[audio-stream-controller]');
+    super(
+      hls,
+      fragmentTracker,
+      keyLoader,
+      '[audio-stream-controller]',
+      PlaylistLevelType.AUDIO
+    );
     this._registerListeners();
   }
 
@@ -309,9 +315,9 @@ class AudioStreamController
     if (bufferInfo === null) {
       return;
     }
-    const audioSwitch = !!this.switchingTrack;
+    const { bufferedTrack, switchingTrack } = this;
 
-    if (!audioSwitch && this._streamEnded(bufferInfo, trackDetails)) {
+    if (!switchingTrack && this._streamEnded(bufferInfo, trackDetails)) {
       hls.trigger(Events.BUFFER_EOS, { type: 'audio' });
       this.state = State.ENDED;
       return;
@@ -325,16 +331,18 @@ class AudioStreamController
     const maxBufLen = this.getMaxBufferLength(mainBufferInfo?.len);
 
     // if buffer length is less than maxBufLen try to load a new fragment
-    if (bufferLen >= maxBufLen && !audioSwitch) {
+    if (bufferLen >= maxBufLen && !switchingTrack) {
       return;
     }
     const fragments = trackDetails.fragments;
     const start = fragments[0].start;
     let targetBufferTime = bufferInfo.end;
 
-    if (audioSwitch && media) {
+    if (switchingTrack && media) {
       const pos = this.getLoadPosition();
-      targetBufferTime = pos;
+      if (bufferedTrack && switchingTrack.attrs !== bufferedTrack.attrs) {
+        targetBufferTime = pos;
+      }
       // if currentTime (pos) is less than alt audio playlist start time, it means that alt audio is ahead of currentTime
       if (trackDetails.PTSKnown && pos < start) {
         // if everything is buffered from pos to start or if audio buffer upfront, let's seek to start
@@ -431,7 +439,7 @@ class AudioStreamController
 
     if (fragCurrent) {
       fragCurrent.abortRequests();
-      this.fragmentTracker.removeFragment(fragCurrent);
+      this.removeUnbufferedFrags(fragCurrent.start);
     }
     this.resetLoadingState();
     // destroy useless transmuxer when switching audio to main
@@ -541,12 +549,13 @@ class AudioStreamController
 
     const track = levels[trackId] as Level;
     if (!track) {
-      this.warn('Audio track is defined on fragment load progress');
+      this.warn('Audio track is undefined on fragment load progress');
       return;
     }
     const details = track.details as LevelDetails;
     if (!details) {
       this.warn('Audio track details undefined on fragment load progress');
+      this.removeUnbufferedFrags(frag.start);
       return;
     }
     const audioCodec =
@@ -731,10 +740,7 @@ class AudioStreamController
 
     const context = this.getCurrentContext(chunkMeta);
     if (!context) {
-      this.warn(
-        `The loading context changed while buffering fragment ${chunkMeta.sn} of level ${chunkMeta.level}. This chunk will not be buffered.`
-      );
-      this.resetStartWhenNotLoaded(chunkMeta.level);
+      this.resetWhenMissingContext(chunkMeta);
       return;
     }
     const { frag, part, level } = context;

src/controller/base-stream-controller.ts

@@ -79,6 +79,7 @@ export default class BaseStreamController
   protected fragmentTracker: FragmentTracker;
   protected transmuxer: TransmuxerInterface | null = null;
   protected _state: string = State.STOPPED;
+  protected playlistType: PlaylistLevelType;
   protected media: HTMLMediaElement | null = null;
   protected mediaBuffer: Bufferable | null = null;
   protected config: HlsConfig;
@@ -107,9 +108,11 @@ export default class BaseStreamController
     hls: Hls,
     fragmentTracker: FragmentTracker,
     keyLoader: KeyLoader,
-    logPrefix: string
+    logPrefix: string,
+    playlistType: PlaylistLevelType
   ) {
     super();
+    this.playlistType = playlistType;
     this.logPrefix = logPrefix;
     this.log = logger.log.bind(logger, `${logPrefix}:`);
     this.warn = logger.warn.bind(logger, `${logPrefix}:`);
@@ -270,6 +273,14 @@ export default class BaseStreamController
     }
 
     if (media) {
+      // Remove gap fragments
+      this.fragmentTracker.removeFragmentsInRange(
+        currentTime,
+        Infinity,
+        this.playlistType,
+        true
+      );
+
       this.lastCurrentTime = currentTime;
     }
 
@@ -1587,6 +1598,25 @@ export default class BaseStreamController
     }
   }
 
+  protected resetWhenMissingContext(chunkMeta: ChunkMetadata) {
+    this.warn(
+      `The loading context changed while buffering fragment ${chunkMeta.sn} of level ${chunkMeta.level}. This chunk will not be buffered.`
+    );
+    this.removeUnbufferedFrags();
+    this.resetStartWhenNotLoaded(chunkMeta.level);
+    this.resetLoadingState();
+  }
+
+  protected removeUnbufferedFrags(start: number = 0) {
+    this.fragmentTracker.removeFragmentsInRange(
+      start,
+      Infinity,
+      this.playlistType,
+      false,
+      true
+    );
+  }
+
   private updateLevelTiming(
     frag: Fragment,
     part: Part | null,

src/controller/error-controller.ts

@@ -88,6 +88,7 @@ export default class ErrorController implements NetworkComponentAPI {
     this.unregisterListeners();
     // @ts-ignore
     this.hls = null;
+    this.penalizedRenditions = {};
   }
 
   startLoad(startPosition: number): void {
@@ -328,10 +329,7 @@ export default class ErrorController implements NetworkComponentAPI {
     }
     const level = this.hls.levels[levelIndex];
     if (level) {
-      // No penalty for GAP tags so that player can switch back when GAPs are found in other levels
-      if (data.details !== ErrorDetails.FRAG_GAP) {
-        level.loadError++;
-      }
+      level.loadError++;
       if (hls.autoLevelEnabled) {
         // Search for next level to retry
         let nextLevel = -1;
@@ -476,14 +474,17 @@ export default class ErrorController implements NetworkComponentAPI {
         : hls.loadLevel;
     const level = hls.levels[levelIndex];
     const redundantLevels = level.url.length;
-    this.penalizeRendition(level, data);
+    const errorUrlId = data.frag ? data.frag.urlId : level.urlId;
+    if (level.urlId === errorUrlId && (!data.frag || level.details)) {
+      this.penalizeRendition(level, data);
+    }
     for (let i = 1; i < redundantLevels; i++) {
-      const newUrlId = (level.urlId + i) % redundantLevels;
+      const newUrlId = (errorUrlId + i) % redundantLevels;
       const penalizedRendition = penalizedRenditions[newUrlId];
       // Check if rendition is penalized and skip if it is a bad fit for failover
       if (
         !penalizedRendition ||
-        checkExpired(penalizedRendition, data, penalizedRenditions[level.urlId])
+        checkExpired(penalizedRendition, data, penalizedRenditions[errorUrlId])
       ) {
         // delete penalizedRenditions[newUrlId];
         // Update the url id of all levels so that we stay on the same set of variants when level switching

src/controller/fragment-tracker.ts

@@ -37,6 +37,7 @@ export class FragmentTracker implements ComponentAPI {
 
   private bufferPadding: number = 0.2;
   private hls: Hls;
+  private hasGaps: boolean = false;
 
   constructor(hls: Hls) {
     this.hls = hls;
@@ -220,7 +221,7 @@ export class FragmentTracker implements ComponentAPI {
     }
   }
 
-  public fragBuffered(frag: Fragment, force?: boolean) {
+  public fragBuffered(frag: Fragment, force?: true) {
     const fragKey = getFragmentKey(frag);
     let fragmentEntity = this.fragments[fragKey];
     if (!fragmentEntity && force) {
@@ -231,6 +232,9 @@ export class FragmentTracker implements ComponentAPI {
         buffered: false,
         range: Object.create(null),
       };
+      if (frag.gap) {
+        this.hasGaps = true;
+      }
     }
     if (fragmentEntity) {
       fragmentEntity.loaded = null;
@@ -447,22 +451,28 @@ export class FragmentTracker implements ComponentAPI {
   public removeFragmentsInRange(
     start: number,
     end: number,
-    playlistType: PlaylistLevelType
+    playlistType: PlaylistLevelType,
+    withGapOnly?: boolean,
+    unbufferedOnly?: boolean
   ) {
+    if (withGapOnly && !this.hasGaps) {
+      return;
+    }
     Object.keys(this.fragments).forEach((key) => {
       const fragmentEntity = this.fragments[key];
       if (!fragmentEntity) {
         return;
       }
-      if (fragmentEntity.buffered) {
-        const frag = fragmentEntity.body;
-        if (
-          frag.type === playlistType &&
-          frag.start < end &&
-          frag.end > start
-        ) {
-          this.removeFragment(frag);
-        }
+      const frag = fragmentEntity.body;
+      if (frag.type !== playlistType || (withGapOnly && !frag.gap)) {
+        return;
+      }
+      if (
+        frag.start < end &&
+        frag.end > start &&
+        (fragmentEntity.buffered || unbufferedOnly)
+      ) {
+        this.removeFragment(frag);
       }
     });
   }
@@ -485,6 +495,7 @@ export class FragmentTracker implements ComponentAPI {
     this.endListFragments = Object.create(null);
     this.mainFragEntity = null;
     this.activeParts = null;
+    this.hasGaps = false;
   }
 }
 

src/controller/gap-controller.ts

@@ -1,6 +1,7 @@
 import type { BufferInfo } from '../utils/buffer-helper';
 import { BufferHelper } from '../utils/buffer-helper';
 import { ErrorTypes, ErrorDetails } from '../errors';
+import { PlaylistLevelType } from '../types/loader';
 import { Events } from '../events';
 import { logger } from '../utils/logger';
 import type Hls from '../hls';
@@ -256,7 +257,46 @@ export default class GapController {
       const bufferStarved = bufferInfo.len <= config.maxBufferHole;
       const waiting =
         bufferInfo.len > 0 && bufferInfo.len < 1 && media.readyState < 3;
-      if (currentTime < startTime && (bufferStarved || waiting)) {
+      const gapLength = startTime - currentTime;
+      if (gapLength > 0 && (bufferStarved || waiting)) {
+        // Only allow large gaps to be skipped if it is a start gap, or all fragments in skip range are partial
+        if (gapLength > config.maxBufferHole) {
+          const { fragmentTracker } = this;
+          let startGap = false;
+          if (currentTime === 0) {
+            const startFrag = fragmentTracker.getAppendedFrag(
+              0,
+              PlaylistLevelType.MAIN
+            );
+            if (startFrag && startTime < startFrag.end) {
+              startGap = true;
+            }
+          }
+          if (!startGap) {
+            const startProvisioned =
+              partial ||
+              fragmentTracker.getAppendedFrag(
+                currentTime,
+                PlaylistLevelType.MAIN
+              );
+            if (startProvisioned) {
+              let moreToLoad = false;
+              let pos = startProvisioned.end;
+              while (pos < startTime) {
+                const provisioned = fragmentTracker.getPartialFragment(pos);
+                if (provisioned) {
+                  pos += provisioned.duration;
+                } else {
+                  moreToLoad = true;
+                  break;
+                }
+              }
+              if (moreToLoad) {
+                return 0;
+              }
+            }
+          }
+        }
         const targetTime = Math.max(
           startTime + SKIP_BUFFER_RANGE_START,
           currentTime + SKIP_BUFFER_HOLE_STEP_SECONDS

src/controller/level-helper.ts

@@ -88,10 +88,13 @@ export function updateFragPTSDTS(
     endPTS = Math.max(endPTS, fragEndPts);
     endDTS = Math.max(endDTS, frag.endDTS);
   }
-  frag.duration = endPTS - startPTS;
 
   const drift = startPTS - frag.start;
-  frag.start = frag.startPTS = startPTS;
+  if (frag.start !== 0) {
+    frag.start = startPTS;
+  }
+  frag.duration = endPTS - frag.start;
+  frag.startPTS = startPTS;
   frag.maxStartPTS = maxStartPTS;
   frag.startDTS = startDTS;
   frag.endPTS = endPTS;