fix(dash): [PKG-DASH-05] align nullable SDK metadata and validate real types

packages/artplayer-plugin-dash-control/README.md

@@ -6,6 +6,27 @@ Accepts a caller-owned dash.js instance at `art.dash`. Quality selection adapts
 dash.js 4.x quality methods or 5.x representation methods. Version 5 selection uses
 representation IDs so bitrate filtering does not change the selected quality.
 
+## TypeScript
+
+The formatter receives the original SDK object. For dash.js 5.2.1 types:
+
+```ts
+import type { MediaInfo, Representation } from 'dashjs'
+import dashControl from 'artplayer-plugin-dash-control'
+
+dashControl<Representation, MediaInfo>({
+  quality: { getName: level => `${level.height}p` },
+  audio: { getName: track => track.lang || String(track.id) },
+})
+```
+
+dash.js 4.5.2 uses `BitrateInfo` for quality instead of `Representation`. Audio
+metadata `id`, `index`, and `lang` may be null; custom formatters must return strings.
+The original object-based formatters and synchronous `update()` remain supported.
+Actual 5.2.1 SDK types resolve with TypeScript 5.9.3 NodeNext/Bundler in our matrix;
+Node10 resolution and TypeScript 4.3.5 have upstream SDK declaration limitations.
+See the [tested type matrix](../../refactor/changes/2026-09-12-PKG-DASH-05-sdk-types.md).
+
 ## Demo
 
 [https://artplayer.org](https://artplayer.org/?libs=https://cdnjs.cloudflare.com/ajax/libs/dashjs/5.2.1/modern/umd/dash.all.min.js%0A./uncompiled/artplayer-plugin-dash-control/index.js&example=dash.control)