Fix seeking into and over multiple EXT-X-GAP segments (video-dev#6988)

* Fix seeking into and over multiple EXT-X-GAP segments
Fixes video-dev#6814

* Add `hls.loadLevelObj` to API - replaces internal use of `hls.levels[hls.loadLevel]`

Author: robwalch

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

@@ -1866,7 +1866,7 @@ export class FragmentTracker implements ComponentAPI {
     getBufferedFrag(position: number, levelType: PlaylistLevelType): MediaFragment | null;
     // (undocumented)
     getFragAtPos(position: number, levelType: PlaylistLevelType, buffered?: boolean): MediaFragment | null;
-    getPartialFragment(time: number): Fragment | null;
+    getPartialFragment(time: number): MediaFragment | null;
     // (undocumented)
     getState(fragment: Fragment): FragmentState;
     // (undocumented)
@@ -2019,6 +2019,8 @@ class Hls implements HlsEventEmitter {
     get loadLevel(): number;
     // Warning: (ae-setter-with-docs) The doc comment for the property "loadLevel" must appear on the getter, not the setter.
     set loadLevel(newLevel: number);
+    // (undocumented)
+    get loadLevelObj(): Level | null;
     loadSource(url: string): void;
     readonly logger: ILogger;
     get lowLatencyMode(): boolean;

docs/API.md

@@ -190,6 +190,7 @@ See [API Reference](https://hlsjs-dev.video-dev.org/api-docs/) for a complete li
   - [Interstitial Objects and Classes](#interstitial-objects-and-classes)
 - [Additional data](#additional-data)
   - [`hls.latestLevelDetails`](#hlslatestleveldetails)
+  - [`hjs.loadLevelObj`](#hjsloadlevelobj)
   - [`hls.sessionId`](#hlssessionid)
 - [Runtime Events](#runtime-events)
 - [Creating a Custom Loader](#creating-a-custom-loader)
@@ -2145,7 +2146,11 @@ type InterstitialAssetErrorData = {
 
 ### `hls.latestLevelDetails`
 
-- get: Returns the LevelDetails of the most up-to-date HLS variant playlist data.
+- get: Returns the `LevelDetails` of last loaded level (variant) or `null` prior to loading a media playlist.
+
+### `hjs.loadLevelObj`
+
+- get: Returns the `Level` object of the selected level (variant) or `null` prior to selecting a level or once the level is removed.
 
 ### `hls.sessionId`
 

src/controller/abr-controller.ts

@@ -672,8 +672,8 @@ class AbrController extends Logger implements AbrComponentAPI {
     }
     // If no matching level found, see if min auto level would be a better option
     const minLevel = hls.levels[minAutoLevel];
-    const autoLevel = hls.levels[hls.loadLevel];
-    if (minLevel?.bitrate < autoLevel?.bitrate) {
+    const autoLevel = hls.loadLevelObj;
+    if (autoLevel && minLevel?.bitrate < autoLevel.bitrate) {
       return minAutoLevel;
     }
     // or if bitrate is not lower, continue to use loadLevel

src/controller/base-stream-controller.ts

@@ -1215,11 +1215,11 @@ export default class BaseStreamController
         bufferedFragAtPos &&
         (bufferInfo.nextStart <= bufferedFragAtPos.end || bufferedFragAtPos.gap)
       ) {
-        return BufferHelper.bufferInfo(
-          bufferable,
-          pos,
-          Math.max(bufferInfo.nextStart, maxBufferHole),
+        const gapDuration = Math.max(
+          Math.min(bufferInfo.nextStart, bufferedFragAtPos.end) - pos,
+          maxBufferHole,
         );
+        return BufferHelper.bufferInfo(bufferable, pos, gapDuration);
       }
     }
     return bufferInfo;

src/controller/error-controller.ts

@@ -176,7 +176,7 @@ export default class ErrorController
       case ErrorDetails.SUBTITLE_LOAD_ERROR:
       case ErrorDetails.SUBTITLE_TRACK_LOAD_TIMEOUT:
         if (context) {
-          const level = hls.levels[hls.loadLevel];
+          const level = hls.loadLevelObj;
           if (
             level &&
             ((context.type === PlaylistContextType.AUDIO_TRACK &&
@@ -200,7 +200,7 @@ export default class ErrorController
         return;
       case ErrorDetails.KEY_SYSTEM_STATUS_OUTPUT_RESTRICTED:
         {
-          const level = hls.levels[hls.loadLevel];
+          const level = hls.loadLevelObj;
           const restrictedHdcpLevel = level?.attrs['HDCP-LEVEL'];
           if (restrictedHdcpLevel) {
             data.errorAction = {

src/controller/fragment-tracker.ts

@@ -321,7 +321,7 @@ export class FragmentTracker implements ComponentAPI {
   /**
    * Gets the partial fragment for a certain time
    */
-  public getPartialFragment(time: number): Fragment | null {
+  public getPartialFragment(time: number): MediaFragment | null {
     let bestFragment: Fragment | null = null;
     let timePadding: number;
     let startTime: number;

src/controller/gap-controller.ts

@@ -12,7 +12,7 @@ import type { InFlightData } from './base-stream-controller';
 import type { InFlightFragments } from '../hls';
 import type Hls from '../hls';
 import type { FragmentTracker } from './fragment-tracker';
-import type { Fragment } from '../loader/fragment';
+import type { Fragment, MediaFragment } from '../loader/fragment';
 import type { SourceBufferName } from '../types/buffer';
 import type {
   BufferAppendedData,
@@ -503,7 +503,7 @@ export default class GapController extends TaskLoop {
    * @param partial - The partial fragment found at the current time (where playback is stalling).
    * @private
    */
-  private _trySkipBufferHole(partial: Fragment | null): number {
+  private _trySkipBufferHole(partial: MediaFragment | null): number {
     const { fragmentTracker, media } = this;
     const config = this.hls?.config;
     if (!media || !fragmentTracker || !config) {
@@ -515,7 +515,7 @@ export default class GapController extends TaskLoop {
     const bufferInfo = BufferHelper.bufferInfo(media, currentTime, 0);
     const startTime =
       currentTime < bufferInfo.start ? bufferInfo.start : bufferInfo.nextStart;
-    if (startTime) {
+    if (startTime && this.hls) {
       const bufferStarved = bufferInfo.len <= config.maxBufferHole;
       const waiting =
         bufferInfo.len > 0 && bufferInfo.len < 1 && media.readyState < 3;
@@ -541,6 +541,19 @@ export default class GapController extends TaskLoop {
                 PlaylistLevelType.MAIN,
               );
             if (startProvisioned) {
+              // Do not seek when selected variant playlist is unloaded
+              if (!this.hls.loadLevelObj?.details) {
+                return 0;
+              }
+              // Do not seek when required fragments are inflight or appending
+              const inFlightDependency = getInFlightDependency(
+                this.hls.inFlightFragments,
+                startTime,
+              );
+              if (inFlightDependency) {
+                return 0;
+              }
+              // Do not seek if we can't walk tracked fragments to end of gap
               let moreToLoad = false;
               let pos = startProvisioned.end;
               while (pos < startTime) {
@@ -567,7 +580,7 @@ export default class GapController extends TaskLoop {
         );
         this.moved = true;
         media.currentTime = targetTime;
-        if (!partial?.gap && this.hls) {
+        if (!partial?.gap) {
           const error = new Error(
             `fragment loaded with buffer holes, seeking from ${currentTime} to ${targetTime}`,
           );

src/controller/interstitials-controller.ts

@@ -1921,7 +1921,7 @@ Schedule: ${scheduleItems.map((seg) => segmentToString(seg))}`,
     const userConfig = primary.userConfig;
     let videoPreference = userConfig.videoPreference;
     const currentLevel =
-      primary.levels[primary.loadLevel] || primary.levels[primary.currentLevel];
+      primary.loadLevelObj || primary.levels[primary.currentLevel];
     if (videoPreference || currentLevel) {
       videoPreference = Object.assign({}, videoPreference);
       if (currentLevel.videoCodec) {

src/controller/level-controller.ts

@@ -389,6 +389,10 @@ export default class LevelController extends BasePlaylistController {
     return this._levels;
   }
 
+  get loadLevelObj(): Level | null {
+    return this.currentLevel;
+  }
+
   get level(): number {
     return this.currentLevelIndex;
   }

src/controller/stream-controller.ts

@@ -237,7 +237,7 @@ export default class StreamController
 
   protected onTickEnd() {
     super.onTickEnd();
-    if (this.media?.readyState) {
+    if (this.media?.readyState && this.media.seeking === false) {
       this.lastCurrentTime = this.media.currentTime;
     }
     this.checkFragmentChanged();

src/hls.ts

@@ -690,10 +690,20 @@ export default class Hls implements HlsEventEmitter {
     return levels ? levels : [];
   }
 
+  /**
+   * @returns LevelDetails of last loaded level (variant) or `null` prior to loading a media playlist.
+   */
   get latestLevelDetails(): LevelDetails | null {
     return this.streamController.getLevelDetails() || null;
   }
 
+  /**
+   * @returns Level object of selected level (variant) or `null` prior to selecting a level or once the level is removed.
+   */
+  get loadLevelObj(): Level | null {
+    return this.levelController.loadLevelObj;
+  }
+
   /**
    * Index of quality level (variant) currently played
    */

src/utils/rendition-helper.ts

@@ -502,5 +502,5 @@ export function useAlternateAudio(
   audioTrackUrl: string | undefined,
   hls: Hls,
 ): boolean {
-  return !!audioTrackUrl && audioTrackUrl !== hls.levels[hls.loadLevel]?.uri;
+  return !!audioTrackUrl && audioTrackUrl !== hls.loadLevelObj?.uri;
 }

tests/unit/controller/gap-controller.ts

@@ -16,7 +16,7 @@ import {
 import { MockMediaElement, MockMediaSource } from '../utils/mock-media';
 import type { HlsConfig } from '../../../src/config';
 import type StreamController from '../../../src/controller/stream-controller';
-import type { Fragment } from '../../../src/loader/fragment';
+import type { Fragment, MediaFragment } from '../../../src/loader/fragment';
 
 chai.use(sinonChai);
 const expect = chai.expect;
@@ -202,7 +202,7 @@ describe('GapController', function () {
       const bufferInfo = BufferHelper.bufferedInfo([], 0, 0);
       sandbox
         .stub(gapController.fragmentTracker, 'getPartialFragment')
-        .returns({} as unknown as Fragment);
+        .returns({} as unknown as MediaFragment);
       const skipHoleStub = sandbox.stub(gapController, '_trySkipBufferHole');
       gapController._tryFixBufferStall(bufferInfo, 100);
       expect(skipHoleStub).to.have.been.calledOnce;