diff --git a/.escheckrc b/.escheckrc
index d60c2b4ffed..292697b2673 100644
--- a/.escheckrc
+++ b/.escheckrc
@@ -1,7 +1,38 @@
-{
-  "ecmaVersion": "es5",
-  "modules": "false",
-  "files": [
-    "./dist/**/*.js"
-  ]
-}
+[
+  {
+    "ecmaVersion": "es5",
+    "module": false,
+    "files": [
+      "./dist/hls.js",
+      "./dist/hls.min.js",
+      "./dist/hls.light.js",
+      "./dist/hls.light.min.js",
+      "./dist/hls.worker.js"
+    ]
+  },
+  {
+    "ecmaVersion": "es2016",
+    "module": false,
+    "checkFeatures": true,
+    "ignore": "globalThis,ErrorCause",
+    "files": [
+      "./dist/hls.light.js",
+      "./dist/hls.light.min.js",
+      "./dist/hls.worker.js"
+    ]
+  },
+  {
+    "ecmaVersion": "es2017",
+    "module": false,
+    "checkFeatures": true,
+    "ignore": "globalThis,ErrorCause",
+    "files": ["./dist/hls.js", "./dist/hls.min.js"]
+  },
+  {
+    "ecmaVersion": "es2017",
+    "module": true,
+    "checkFeatures": true,
+    "ignore": "globalThis,ErrorCause",
+    "files": ["./dist/hls.mjs", "./dist/hls.light.mjs"]
+  }
+]
diff --git a/.eslintrc.js b/.eslintrc.js
index ccce4ebb48a..4b084bb03a8 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -2,12 +2,23 @@ const asyncKeywordConstraintMsg =
   'The async keyword adds a `regenerator` dependency in the hls.js ES5 output not allowed in v1 due to bundle size constraints.';
 const selfVsWindowGlobalMsg =
   'Use `self` instead of `window` to access the global context everywhere (including workers).';
-const arrayFindCompatibilityMsg =
-  'Usage of Array find method is restricted for compatibility.';
-const arrayFindIndexCompatibilityMsg =
-  'Usage of Array findIndex method is restricted for compatibility.';
-const arrayEveryCompatibilityMsg =
-  'Usage of Array every method is restricted for compatibility. Use a negative Array some check instead.';
+const arrayIncludesCompatibilityMsg =
+  'Usage of Array includes method is restricted for compatibility. Use Array indexOf instead. (For String includes, suppress this with an eslint-disable comment.)';
+
+const baseRestrictedSyntax = [
+  {
+    selector: 'FunctionDeclaration[async=true]',
+    message: asyncKeywordConstraintMsg,
+  },
+  {
+    selector: 'ArrowFunctionExpression[async=true]',
+    message: asyncKeywordConstraintMsg,
+  },
+  {
+    selector: 'MethodDefinition[value.async=true]',
+    message: asyncKeywordConstraintMsg,
+  },
+];
 
 module.exports = {
   env: { browser: true, commonjs: true, es6: true },
@@ -31,6 +42,7 @@ module.exports = {
   // see https://github.com/standard/eslint-config-standard
   // 'prettier' (https://github.com/prettier/eslint-config-prettier) must be last
   extends: ['eslint:recommended', 'prettier'],
+  ignorePatterns: ['dist/'],
   parser: '@typescript-eslint/parser',
   parserOptions: { sourceType: 'module', project: './tsconfig.json' },
   plugins: ['@typescript-eslint', 'import', 'no-for-of-loops'],
@@ -74,32 +86,11 @@ module.exports = {
         'no-use-before-define': 'off',
         'no-restricted-syntax': [
           'error',
-          {
-            selector: 'FunctionDeclaration[async=true]',
-            message: asyncKeywordConstraintMsg,
-          },
-          {
-            selector: 'ArrowFunctionExpression[async=true]',
-            message: asyncKeywordConstraintMsg,
-          },
-          {
-            selector: 'MethodDefinition[value.async=true]',
-            message: asyncKeywordConstraintMsg,
-          },
+          ...baseRestrictedSyntax,
           {
             selector:
-              'MemberExpression[property.name="find"][object.type="Identifier"]',
-            message: arrayFindCompatibilityMsg,
-          },
-          {
-            selector:
-              'MemberExpression[property.name="findIndex"][object.type="Identifier"]',
-            message: arrayFindIndexCompatibilityMsg,
-          },
-          {
-            selector:
-              'MemberExpression[property.name="every"][object.type="Identifier"]',
-            message: arrayEveryCompatibilityMsg,
+              'MemberExpression[property.name="includes"][object.type="Identifier"]',
+            message: arrayIncludesCompatibilityMsg,
           },
         ],
         'import/order': [
@@ -137,5 +128,14 @@ module.exports = {
         '@typescript-eslint/no-misused-promises': 'error',
       },
     },
+    {
+      files: ['tests/**/*.ts'],
+      rules: {
+        // Tests run only in modern browsers and aren't bundled, so the
+        // Array.includes compatibility constraint that applies to src/ doesn't
+        // apply here.
+        'no-restricted-syntax': ['error', ...baseRestrictedSyntax],
+      },
+    },
   ],
 };
diff --git a/README.md b/README.md
index cd53893fe37..734000c0255 100644
--- a/README.md
+++ b/README.md
@@ -296,16 +296,27 @@ HLS.js is only compatible with browsers supporting MediaSource extensions (MSE)
 
 HLS.js is supported on:
 
-- Chrome 39+ for Android
-- Chrome 39+ for Desktop
-- Firefox 41+ for Android
-- Firefox 42+ for Desktop
+- Chrome 47+ for Desktop
+- Firefox 51+ for Desktop
 - Edge for Windows 10+
-- Safari 9+ for macOS 10.11+
+- Safari 10+ for macOS 10.11+
 - Safari for iPadOS 13+
 - Safari for iOS 17.1+ since HLS version [1.5.0](https://github.com/video-dev/hls.js/releases/tag/v1.5.0) using Managed Media Source (MMS) [WebKit blog](https://webkit.org/blog/14735/webkit-features-in-safari-17-1/)
+- Chrome for Android 5+
+- Firefox for Android 5+
 
-A [Promise polyfill](https://github.com/taylorhakes/promise-polyfill) is required in browsers missing native promise support.
+These versions are the targets passed to [`@babel/preset-env`](https://babeljs.io/docs/babel-preset-env) when building the UMD bundles in `dist/`. They share an **ES2016 runtime baseline**: ES5-style syntax plus native ES2016 globals (`Map`, `Set`, `Promise`, `Array.from`, `Uint8Array.from`, `Array.prototype.includes`, etc.). To keep bundle size small, no `core-js` polyfills are bundled.
+
+Optional features such as CMCD pull in ES2017 APIs (e.g. `Object.entries`), so the full UMD bundle effectively requires an ES2017-capable runtime. The `light` bundle excludes those features and stays at the ES2016 baseline.
+
+The `dist/` folder ships two distribution variants:
+
+- **UMD** (`dist/hls.js`, `dist/hls.min.js`, `dist/hls.light.js`, `dist/hls.light.min.js`) — embeddable directly via a `<script>` tag (exposes a global `Hls`) or resolved by `require('hls.js')` via `package.json`'s `main` field. Targets the browser list above. The companion `dist/hls.worker.js` is the bundled transmuxer Web Worker.
+- **ESM** (`dist/hls.mjs`, `dist/hls.light.mjs`) — resolved by `import 'hls.js'` via the `module` field. Built with `@babel/preset-env`'s `esmodules: true` target (≈ Chrome 61+, Firefox 60+, Safari 10.1+, Edge 16+) and intended to be consumed by a modern bundler. Uses ES2015+ syntax but stays below ES2019 (no `Array.prototype.flatMap`, `Object.fromEntries`, etc.).
+
+If you import from `src/` directly or include any of our runtime dependencies untranspiled in your own build, you bypass this Babel pipeline and become responsible for transpilation; those source modules can reach for ES2019+ APIs that are tree-shaken out of the bundles we publish.
+
+To run on browsers below this baseline, supply your own polyfills for any missing globals before HLS.js loads.
 
 **Please note:**
 
diff --git a/build-config.js b/build-config.js
index 91c1afbb71e..d23b287984c 100644
--- a/build-config.js
+++ b/build-config.js
@@ -126,12 +126,17 @@ const workerFnFooter = '})(false);';
 
 const extensions = ['.ts', '.js'];
 
+// Browser baseline for the legacy UMD/IIFE bundles. Chosen so that all listed
+// targets natively support the ES2015 built-ins (Map, Set, Array.from,
+// Uint8Array.from, Promise, etc.) that source and bundled @svta/* deps rely
+// on — we intentionally do NOT bundle core-js polyfills, to keep size down.
+// Keep this list in sync with the "Compatibility" section in README.md.
 const babelPresetEnvTargets = {
   chrome: '47',
   firefox: '51',
-  safari: '8',
-  ios: '8',
-  android: '4',
+  safari: '10',
+  ios: '10',
+  android: '5',
   samsung: '5',
   edge: '14',
 };
diff --git a/src/controller/eme-controller.ts b/src/controller/eme-controller.ts
index bcff60dc65d..e09f0216c4f 100644
--- a/src/controller/eme-controller.ts
+++ b/src/controller/eme-controller.ts
@@ -1368,6 +1368,7 @@ class EMEController extends Logger implements ComponentAPI {
       null,
       new Uint16Array(licenseChallenge.buffer),
     );
+    // eslint-disable-next-line no-restricted-syntax
     if (!xmlString.includes('PlayReadyKeyMessage')) {
       // This does not appear to be a wrapped message as on Edge.  Some
       // clients do not need this unwrapping, so we will assume this is one of
diff --git a/src/controller/id3-track-controller.ts b/src/controller/id3-track-controller.ts
index f9c6e16cf3f..6a5c6a41a79 100644
--- a/src/controller/id3-track-controller.ts
+++ b/src/controller/id3-track-controller.ts
@@ -360,7 +360,7 @@ export class ID3TrackController implements ComponentAPI {
     if (id3Track && removeOldCues) {
       if (id3Track.track.cues?.length) {
         const idsToRemove = Object.keys(dateRangeCuesAppended).filter(
-          (id) => !ids.includes(id),
+          (id) => ids.indexOf(id) === -1,
         );
         for (let i = idsToRemove.length; i--; ) {
           const id = idsToRemove[i];
diff --git a/src/controller/interstitials-controller.ts b/src/controller/interstitials-controller.ts
index 0cd98c507f3..a11a2d730cf 100644
--- a/src/controller/interstitials-controller.ts
+++ b/src/controller/interstitials-controller.ts
@@ -1789,7 +1789,7 @@ Schedule: ${scheduleItems.map((seg) => segmentToString(seg))} pos: ${this.timeli
 
       if (
         this.isInterstitial(playingItem) &&
-        removedIds.includes(playingItem.event.identifier)
+        removedIds.indexOf(playingItem.event.identifier) > -1
       ) {
         this.warn(
           `Interstitial "${playingItem.event.identifier}" removed while playing`,
diff --git a/src/controller/interstitials-schedule.ts b/src/controller/interstitials-schedule.ts
index af1d20af70d..3c396238aea 100644
--- a/src/controller/interstitials-schedule.ts
+++ b/src/controller/interstitials-schedule.ts
@@ -258,7 +258,7 @@ export class InterstitialsSchedule extends Logger {
     const ids = Object.keys(dateRanges);
     const removedInterstitials = previousInterstitialEvents
       ? previousInterstitialEvents.filter(
-          (event) => !ids.includes(event.identifier),
+          (event) => ids.indexOf(event.identifier) === -1,
         )
       : [];
     if (interstitialEvents.length) {
diff --git a/src/controller/subtitle-track-controller.ts b/src/controller/subtitle-track-controller.ts
index deef87ed33f..91b5e18a46a 100644
--- a/src/controller/subtitle-track-controller.ts
+++ b/src/controller/subtitle-track-controller.ts
@@ -268,7 +268,7 @@ class SubtitleTrackController extends BasePlaylistController {
             ? this.hls.config.enableIMSC1
             : this.hls.config.enableWebVTT
         ) {
-          if (!subtitleGroups || subtitleGroups.includes(track.groupId)) {
+          if (!subtitleGroups || subtitleGroups.indexOf(track.groupId) > -1) {
             // track.id should match hls.subtitleTracks index
             track.id = subtitleTracks.length;
             subtitleTracks.push(track);
diff --git a/src/remux/mp4-remuxer.ts b/src/remux/mp4-remuxer.ts
index 4225719608f..1ff0a7e1b3b 100644
--- a/src/remux/mp4-remuxer.ts
+++ b/src/remux/mp4-remuxer.ts
@@ -245,7 +245,7 @@ export default class MP4Remuxer extends Logger implements Remuxer {
       }
 
       if (this.ISGenerated) {
-        if (enoughAudioSamples && enoughVideoSamples) {
+        if (enoughAudioSamples && enoughVideoSamples && timeOffset) {
           // timeOffset is expected to be the offset of the first timestamp of this fragment (first DTS)
           // if first audio DTS is not aligned with first video DTS then we need to take that into account
           // when providing timeOffset to remuxAudio / remuxVideo. if we don't do that, there might be a permanent / small
@@ -482,7 +482,8 @@ export default class MP4Remuxer extends Logger implements Remuxer {
           (timeOffset === 0 && videoInitPTS < _initPTS.baseTime)
         ) {
           initDTS = Math.min(initDTS as number, videoInitDTS);
-          initPTS = Math.min(initPTS as number, videoInitPTS);
+          // Bind initPTS to the lowest DTS across tracks to prevent negative timestamps
+          initPTS = Math.min(initPTS as number, videoInitDTS);
         }
       }
       this.videoTrackConfig = {