Merge pull request #4806 from video-dev/bugfix/wait-for-active-fragment-before-gap-seek

Make gap controller wait for active fragments while seeking

Author: robwalch

src/controller/gap-controller.ts

@@ -5,8 +5,8 @@ import { Events } from '../events';
 import { logger } from '../utils/logger';
 import type Hls from '../hls';
 import type { HlsConfig } from '../config';
+import type { Fragment } from '../loader/fragment';
 import type { FragmentTracker } from './fragment-tracker';
-import { Fragment } from '../loader/fragment';
 
 export const STALL_MINIMUM_DURATION_MS = 250;
 export const MAX_START_GAP_JUMP = 2.0;
@@ -43,7 +43,7 @@ export default class GapController {
    *
    * @param {number} lastCurrentTime Previously read playhead position
    */
-  public poll(lastCurrentTime: number) {
+  public poll(lastCurrentTime: number, activeFrag: Fragment | null) {
     const { config, media, stalled } = this;
     if (media === null) {
       return;
@@ -104,6 +104,7 @@ export default class GapController {
       // Next buffered range is too far ahead to jump to while still seeking
       const noBufferGap =
         !nextStart ||
+        (activeFrag && activeFrag.start <= currentTime) ||
         (nextStart - currentTime > MAX_START_GAP_JUMP &&
           !this.fragmentTracker.getPartialFragment(currentTime));
       if (hasEnoughBuffer || noBufferGap) {

src/controller/stream-controller.ts

@@ -925,7 +925,8 @@ export default class StreamController
       this.seekToStartPos();
     } else {
       // Resolve gaps using the main buffer, whose ranges are the intersections of the A/V sourcebuffers
-      gapController.poll(this.lastCurrentTime);
+      const activeFrag = this.state !== State.IDLE ? this.fragCurrent : null;
+      gapController.poll(this.lastCurrentTime, activeFrag);
     }
 
     this.lastCurrentTime = media.currentTime;

tests/unit/controller/gap-controller.js

@@ -269,6 +269,30 @@ describe('GapController', function () {
       wallClock.tick(2 * STALL_HANDLING_RETRY_PERIOD_MS);
     });
 
+    it('should not detect stalls when loading an earlier fragment while seeking', function () {
+      wallClock.tick(2 * STALL_HANDLING_RETRY_PERIOD_MS);
+      mockMedia.currentTime += 0.1;
+      gapController.poll(0);
+      expect(gapController.stalled).to.equal(null, 'buffered start');
+
+      wallClock.tick(2 * STALL_HANDLING_RETRY_PERIOD_MS);
+      mockMedia.currentTime += 5;
+      mockMedia.seeking = true;
+      mockTimeRangesData.length = 1;
+      mockTimeRangesData[0] = [5.5, 10];
+      gapController.poll(mockMedia.currentTime - 5);
+      expect(gapController.stalled).to.equal(null, 'new seek position');
+
+      wallClock.tick(2 * STALL_HANDLING_RETRY_PERIOD_MS);
+      gapController.poll(mockMedia.currentTime, {
+        start: 5,
+      });
+      expect(gapController.stalled).to.equal(
+        null,
+        'seeking while loading fragment'
+      );
+    });
+
     it('should trigger reportStall when stalling for 250ms or longer', function () {
       setStalling();
       wallClock.tick(250);