Reload live stream using last segment length when distance to playlis…

…t end is less than or equal to four target durations

(Reload is scheduled on update. With a default live sync of 3 target durations, without interruption, a distance of 3x-4x is most likely.)

src/controller/level-helper.ts

@@ -7,7 +7,6 @@ import { logger } from '../utils/logger';
 import { Fragment, Part } from '../loader/fragment';
 import { LevelDetails } from '../loader/level-details';
 import type { Level } from '../types/level';
-import type { LoaderStats } from '../types/loader';
 import type { MediaPlaylist } from '../types/media-playlist';
 import { DateRange } from '../loader/date-range';
 
@@ -441,7 +440,11 @@ export function computeReloadInterval(
   if (newDetails.updated) {
     // Use last segment duration when shorter than target duration and near live edge
     const fragments = newDetails.fragments;
-    if (fragments.length && reloadInterval * 3 > distanceToLiveEdgeMs) {
+    const liveEdgeMaxTargetDurations = 4;
+    if (
+      fragments.length &&
+      reloadInterval * liveEdgeMaxTargetDurations > distanceToLiveEdgeMs
+    ) {
       const lastSegmentDuration =
         fragments[fragments.length - 1].duration * 1000;
       if (lastSegmentDuration < reloadInterval) {

tests/unit/controller/level-helper.ts

@@ -307,11 +307,11 @@ expect: ${JSON.stringify(merged.fragments[i])}`
       expect(actual).to.equal(2500);
     });
 
-    it('returns the last fragment duration when distance to live edge is less than three target durations', function () {
+    it('returns the last fragment duration when distance to live edge is less than or equal to four target durations', function () {
       const newPlaylist = generatePlaylist([3, 4], 0, 2);
       newPlaylist.targetduration = 5;
       newPlaylist.updated = true;
-      const actual = computeReloadInterval(newPlaylist, 15000);
+      const actual = computeReloadInterval(newPlaylist, 20000);
       expect(actual).to.equal(5000);
       const actualLow = computeReloadInterval(newPlaylist, 14000);
       expect(actualLow).to.equal(2000);