Fix Live Interstitial midroll buffering and playback (#7913)

* Fix midroll buffering and playback progression from preroll at live edge
Fixes #7912

* Fix live midroll interstitial resumption (low-latency and short primary breaks)
#7912

* Fix appendInPlace stall handling
#7912

* Replace `advanceInPlace` with `hls.startLoad`

* Fix live midroll interstitial resumption (low-latency and short primary breaks)
- Ensure seek to start on midroll join
- Prevent lastCurrentTime > startPosition lock-in before segments are parsed
- Improve live primary resumption estimate at end of interstitial playback
Resolves #7912

Author: robwalch

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

@@ -2419,7 +2419,7 @@ export class HlsAssetPlayer {
     // (undocumented)
     get bufferedEnd(): number;
     // (undocumented)
-    bufferedInPlaceToEnd(media?: HTMLMediaElement | null): boolean;
+    bufferedInPlaceToEnd(media?: HTMLMediaElement | null, fromTime?: number): boolean;
     // (undocumented)
     get currentTime(): number;
     // (undocumented)

src/controller/audio-stream-controller.ts

@@ -222,20 +222,29 @@ class AudioStreamController
     const lastCurrentTime = this.lastCurrentTime;
     this.stopLoad();
     this.setInterval(TICK_INTERVAL);
-    if (lastCurrentTime > 0 && startPosition === -1) {
+    if (
+      lastCurrentTime > 0 &&
+      startPosition === -1 &&
+      !skipSeekToStartPosition &&
+      this.initPTS.length
+    ) {
       this.log(
         `Override startPosition with lastCurrentTime @${lastCurrentTime.toFixed(
           3,
         )}`,
       );
       startPosition = lastCurrentTime;
-      this.state = State.IDLE;
-    } else {
-      this.state = State.WAITING_TRACK;
     }
+    this.state = State.IDLE;
     this.nextLoadPosition = this.lastCurrentTime =
       startPosition + this.timelineOffset;
     this.startPosition = skipSeekToStartPosition ? -1 : startPosition;
+    if (
+      !skipSeekToStartPosition &&
+      !this.fragmentTracker.hasFragments(this.playlistType)
+    ) {
+      this.startFragRequested = false;
+    }
     this.tick();
   }
 

src/controller/base-stream-controller.ts

@@ -3,6 +3,7 @@ import {
   findFragmentByPDT,
   findFragmentByPTS,
   findNearestWithCC,
+  getNextFrag,
 } from './fragment-finders';
 import { FragmentState } from './fragment-tracker';
 import Decrypter from '../crypt/decrypter';
@@ -1603,7 +1604,10 @@ export default class BaseStreamController
     }
     let programFrag = this.filterReplacedPrimary(frag, levelDetails);
     if (!programFrag && frag) {
-      programFrag = fragments[1 + frag.sn - levelDetails.startSN] || null;
+      programFrag = getNextFrag(levelDetails, frag.sn, this.loadingParts);
+      if (programFrag) {
+        this.nextLoadPosition = programFrag.start;
+      }
     }
     return programFrag;
   }
@@ -1696,9 +1700,9 @@ export default class BaseStreamController
         if (bufferingInterstitial) {
           // Do not stream fragments while buffering Interstitial Events (except for overlap at the start)
           if (
-            bufferingInterstitial.appendInPlace ||
-            Math.abs(frag.start - bufferingItem.start) > 1 ||
-            bufferingItem.start === 0
+            !bufferingInterstitial.appendInPlace &&
+            (Math.abs(frag.start - bufferingItem.start) > 1 ||
+              bufferingItem.start === 0)
           ) {
             return null;
           }
@@ -1713,7 +1717,8 @@ export default class BaseStreamController
             // fragment is past schedule item end
             // allow some overflow when not appending in place to prevent stalls
             if (
-              bufferingItem.nextEvent.appendInPlace ||
+              (bufferingItem.nextEvent.appendInPlace &&
+                !bufferingItem.nextEvent.hasPlayed) ||
               frag.start - bufferingItem.end > 1
             ) {
               return null;

src/controller/buffer-controller.ts

@@ -837,12 +837,10 @@ transfer tracks: ${stringify(transferredTracks, (key, value) => (key === 'initSe
         const videoAppendEnd = partOrFrag.end;
         const diff = this.lastVideoAppendEnd - videoAppendEnd;
         this.lastVideoAppendEnd = videoAppendEnd;
-        if (this.isAudioBlocked()) {
-          if (diff < 0 || diff > partOrFrag.duration) {
-            this.unblockAudio();
-          } else {
-            this.executeNext('audio');
-          }
+        if (diff < 0 || diff > partOrFrag.duration) {
+          this.unblockAudio();
+        } else if (this.isAudioBlocked()) {
+          this.executeNext('audio');
         }
       }
     }

src/controller/fragment-finders.ts

@@ -239,3 +239,13 @@ export function findNearestWithCC(
   }
   return null;
 }
+
+export function getNextFrag(
+  details: LevelDetails,
+  sn: number,
+  fragmentHintForParts?: boolean,
+): MediaFragment | null {
+  return fragmentHintForParts && sn === details.endSN && details.fragmentHint
+    ? details.fragmentHint
+    : details.fragments[1 + sn - details.startSN] || null;
+}

src/controller/gap-controller.ts

@@ -3,6 +3,7 @@ import {
   interstitialsEnabled,
   State,
 } from './base-stream-controller';
+import { getNextFrag } from './fragment-finders';
 import { ErrorDetails, ErrorTypes } from '../errors';
 import { Events } from '../events';
 import TaskLoop from '../task-loop';
@@ -344,6 +345,15 @@ export default class GapController extends TaskLoop {
       if (!this.media || (!this.hls as any)) {
         return;
       }
+      if (media.currentTime !== currentTime) {
+        const currentTimeBeforeStallEvent = currentTime;
+        currentTime = media.currentTime;
+        this.moved = true;
+        this.log(
+          `currentTime changed ${currentTimeBeforeStallEvent} > ${currentTime}`,
+        );
+        return;
+      }
     }
 
     const bufferedWithHoles = BufferHelper.bufferInfo(
@@ -763,7 +773,7 @@ function withInterstitialBoundary(
     hls.interstitialsManager
   ) {
     const frag = 'type' in appended ? appended : appended.fragment;
-    const nextFrag = levelDetails.fragments[1 + frag.sn - levelDetails.startSN];
+    const nextFrag = getNextFrag(levelDetails, frag.sn, true);
     if (
       nextFrag?.level === frag.level &&
       fragOverlapsQueuedInterstitial(

src/controller/interstitial-player.ts

@@ -92,7 +92,7 @@ export class HlsAssetPlayer {
     }
   }
 
-  bufferedInPlaceToEnd(media?: HTMLMediaElement | null) {
+  bufferedInPlaceToEnd(media?: HTMLMediaElement | null, fromTime?: number) {
     if (!this.appendInPlace) {
       return false;
     }
@@ -103,8 +103,8 @@ export class HlsAssetPlayer {
       return false;
     }
     const duration = Math.min(this._bufferedEosTime || Infinity, this.duration);
-    const start = this.timelineOffset;
-    const bufferInfo = BufferHelper.bufferInfo(media, start, 0);
+    const start = this.timelineOffset + (fromTime || 0);
+    const bufferInfo = BufferHelper.bufferInfo(media, start, 0.02);
     const bufferedEnd = this.getAssetTime(bufferInfo.end);
     return bufferedEnd >= duration - 0.02;
   }