Fix delta updates with discontinuity tags

Fixes #6949

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

@@ -3105,8 +3105,6 @@ export class LevelDetails {
     // (undocumented)
     appliedTimelineOffset?: number;
     // (undocumented)
-    availabilityDelay?: number;
-    // (undocumented)
     averagetargetduration?: number;
     // (undocumented)
     canBlockReload: boolean;

src/loader/level-details.ts

@@ -25,7 +25,6 @@ export class LevelDetails {
   public advancedDateTime?: number;
   public updated: boolean = true;
   public advanced: boolean = true;
-  public availabilityDelay?: number; // Manifest reload synchronization
   public misses: number = 0;
   public startCC: number = 0;
   public startSN: number = 0;
@@ -87,7 +86,6 @@ export class LevelDetails {
     } else {
       this.misses = previous.misses + 1;
     }
-    this.availabilityDelay = previous.availabilityDelay;
   }
 
   get hasProgramDateTime(): boolean {

src/loader/m3u8-parser.ts

@@ -671,7 +671,7 @@ export default class M3U8Parser {
       if (!level.live) {
         lastFragment.endList = true;
       }
-      if (firstFragment && !level.startCC) {
+      if (firstFragment && level.startCC === undefined) {
         level.startCC = firstFragment.cc;
       }
       /**

src/utils/level-helper.ts

@@ -9,7 +9,12 @@ import type { Fragment, MediaFragment, Part } from '../loader/fragment';
 import type { LevelDetails } from '../loader/level-details';
 import type { Level } from '../types/level';
 
-type FragmentIntersection = (oldFrag: Fragment, newFrag: Fragment) => void;
+type FragmentIntersection = (
+  oldFrag: MediaFragment,
+  newFrag: MediaFragment,
+  newFragIndex: number,
+  newFragments: MediaFragment[],
+) => void;
 type PartIntersection = (oldPart: Part, newPart: Part) => void;
 
 export function updatePTS(
@@ -107,7 +112,7 @@ export function updateFragPTSDTS(
   if (!details || sn < details.startSN || sn > details.endSN) {
     return 0;
   }
-  let i;
+  let i: number;
   const fragIdx = sn - details.startSN;
   const fragments = details.fragments;
   // update frag reference in fragments array
@@ -156,18 +161,19 @@ export function mergeDetails(
     delete oldDetails.fragmentHint.endPTS;
   }
   // check if old/new playlists have fragments in common
-  // loop through overlapping SN and update startPTS , cc, and duration if any found
-  let ccOffset = 0;
-  let PTSFrag;
+  // loop through overlapping SN and update startPTS, cc, and duration if any found
+  let PTSFrag: MediaFragment | undefined;
   mapFragmentIntersection(
     oldDetails,
     newDetails,
-    (oldFrag: Fragment, newFrag: Fragment) => {
-      if (oldFrag.relurl) {
-        // Do not compare CC if the old fragment has no url. This is a level.fragmentHint used by LL-HLS parts.
-        // It maybe be off by 1 if it was created before any parts or discontinuity tags were appended to the end
-        // of the playlist.
-        ccOffset = oldFrag.cc - newFrag.cc;
+    (oldFrag, newFrag, newFragIndex, newFragments) => {
+      if (newDetails.skippedSegments) {
+        if (newFrag.cc !== oldFrag.cc) {
+          const ccOffset = oldFrag.cc - newFrag.cc;
+          for (let i = newFragIndex; i < newFragments.length; i++) {
+            newFragments[i].cc += ccOffset;
+          }
+        }
       }
       if (
         Number.isFinite(oldFrag.startPTS) &&
@@ -207,9 +213,10 @@ export function mergeDetails(
     },
   );
 
+  const newFragments = newDetails.fragments;
   const fragmentsToCheck = newDetails.fragmentHint
-    ? newDetails.fragments.concat(newDetails.fragmentHint)
-    : newDetails.fragments;
+    ? newFragments.concat(newDetails.fragmentHint)
+    : newFragments;
   if (currentInitSegment) {
     fragmentsToCheck.forEach((frag) => {
       if (
@@ -223,19 +230,17 @@ export function mergeDetails(
   }
 
   if (newDetails.skippedSegments) {
-    newDetails.deltaUpdateFailed = newDetails.fragments.some((frag) => !frag);
+    newDetails.deltaUpdateFailed = newFragments.some((frag) => !frag);
     if (newDetails.deltaUpdateFailed) {
       logger.warn(
         '[level-helper] Previous playlist missing segments skipped in delta playlist',
       );
       for (let i = newDetails.skippedSegments; i--; ) {
-        newDetails.fragments.shift();
-      }
-      newDetails.startSN = newDetails.fragments[0].sn;
-      if (!newDetails.startCC) {
-        newDetails.startCC = newDetails.fragments[0].cc;
+        newFragments.shift();
       }
+      newDetails.startSN = newFragments[0].sn;
     } else {
+      newDetails.endCC = newFragments[newFragments.length - 1].cc;
       if (newDetails.canSkipDateRanges) {
         newDetails.dateRanges = mergeDateRanges(
           oldDetails.dateRanges,
@@ -260,17 +265,6 @@ export function mergeDetails(
     }
   }
 
-  const newFragments = newDetails.fragments;
-  if (ccOffset) {
-    logger.warn('discontinuity sliding from playlist, take drift into account');
-    for (let i = 0; i < newFragments.length; i++) {
-      newFragments[i].cc += ccOffset;
-    }
-  }
-  if (newDetails.skippedSegments) {
-    newDetails.startCC = newDetails.fragments[0].cc;
-  }
-
   // Merge parts
   mapPartIntersection(
     oldDetails.partList,
@@ -286,10 +280,10 @@ export function mergeDetails(
     updateFragPTSDTS(
       newDetails,
       PTSFrag,
-      PTSFrag.startPTS,
-      PTSFrag.endPTS,
-      PTSFrag.startDTS,
-      PTSFrag.endDTS,
+      PTSFrag.startPTS as number,
+      PTSFrag.endPTS as number,
+      PTSFrag.startDTS as number,
+      PTSFrag.endDTS as number,
     );
   } else {
     // ensure that delta is within oldFragments range
@@ -414,7 +408,7 @@ export function mapFragmentIntersection(
       newFrag = newDetails.fragments[i] = oldFrag;
     }
     if (oldFrag && newFrag) {
-      intersectionFn(oldFrag, newFrag);
+      intersectionFn(oldFrag, newFrag, i, newFrags);
     }
   }
 }

tests/unit/controller/cmcd-controller.ts

@@ -41,24 +41,24 @@ https://dummy.url.com/10905.m4s
 #EXTINF:2,
 https://dummy.url.com/10906.m4s`;
 
-const details = M3U8Parser.parseLevelPlaylist(
-  playlist,
-  url,
-  0,
-  PlaylistLevelType.MAIN,
-  0,
-  null,
-);
-
 const uuidRegex =
   /[a-f\d]{8}-[a-f\d]{4}-4[a-f\d]{3}-[89ab][a-f\d]{3}-[a-f\d]{12}/;
 
-const level = {
-  bitrate: 1000,
-  details,
-};
-
 const setupEach = (cmcd?: CMCDControllerConfig) => {
+  const details = M3U8Parser.parseLevelPlaylist(
+    playlist,
+    url,
+    0,
+    PlaylistLevelType.MAIN,
+    0,
+    null,
+  );
+
+  const level = {
+    bitrate: 1000,
+    details,
+  };
+
   const hls = new Hls({ cmcd }) as any;
   hls.networkControllers.forEach((component) => component.destroy());
   hls.networkControllers.length = 0;
@@ -71,6 +71,8 @@ const setupEach = (cmcd?: CMCDControllerConfig) => {
   // hls.audioTracks = [];
 
   cmcdController = new CMCDController(hls);
+
+  return details;
 };
 
 const base = {
@@ -151,7 +153,7 @@ describe('CMCDController', function () {
       });
 
       it('uses fragment data', function () {
-        setupEach({});
+        const details = setupEach({});
 
         const { url } = applyFragmentData(details.fragments[0]);
 
@@ -162,7 +164,7 @@ describe('CMCDController', function () {
       });
 
       it('uses part data when available', function () {
-        setupEach({});
+        const details = setupEach({});
 
         const { url } = applyFragmentData(
           details.fragments[2],