beautified some ui

android/README.md

@@ -24,6 +24,22 @@ the course service or extracted from subtitle/speech analysis data.
 These defaults match the desktop player's arrow-key workflow while fitting a
 tablet touch screen.
 
+## Sentence Playback Modes
+
+`PlayerConfig.continuousPlayback` controls how playback crosses sentence
+boundaries:
+
+- `true` (default): the video plays continuously through all sentences.
+- `false`: playback stays on the current sentence; when its boundary is
+  reached, playback loops back to the start of the same sentence until the
+  student swipes to the previous/next sentence.
+
+Toggle it at runtime with `controller.setContinuousPlayback(enabled)`.
+
+`controller.playCurrentSentenceAndStop()` plays only the current sentence and
+automatically pauses once it finishes — useful for a "play the reference
+sentence" button in a recording test flow.
+
 ## Basic Integration
 
 ```kotlin
@@ -123,6 +139,63 @@ sdk.videoCatalogApi.fetch(object : VideoCatalogCallback {
 })
 ```
 
+## Sample App Configuration
+
+The sample app points at the cloud service through the `SERVER_BASE_URL`
+constant at the top of `MainActivity.kt`:
+
+```kotlin
+const val SERVER_BASE_URL = "https://videoservice.d1kt.cn"
+```
+
+Change it to your real deployment address before building the APK. For a LAN
+or development server, an `http://<server-ip>:<port>` address works because the
+sample app permits cleartext HTTP (see
+`res/xml/network_security_config.xml`); production should keep HTTPS.
+
+The sample app also enables `allowHttpFallback`: if an `https://` request fails
+with a TLS error (for example a misconfigured or unstable gateway/certificate),
+the SDK automatically retries the same request over plain HTTP. This is a
+convenience for private deployments only — fix the TLS edge in production.
+
+The app has two modules, switched by the `训练` / `测试` tabs at the top:
+
+- `训练`: browse the cloud course list and do sentence-by-sentence playback
+  practice. The old built-in "示例课程" card was removed; only courses served
+  by `GET /api/v1/videos` appear here.
+- `测试`: record your reading of the current sentence and submit it to the
+  server's assessment endpoint for AI scoring. Only cloud courses are
+  supported (the server must know the video hash and reference sentences).
+
+The video's bottom-right corner has a small rotation icon that forces landscape
+or portrait orientation, so rotation works even when the device's auto-rotate
+switch is turned off. The progress bar below the sentence panel is draggable,
+so the student can seek to any position by dragging it.
+
+For the test module, fill in the client key that the server expects in the
+`X-Client-Key` header (the `CLIENT_API_KEY` value from the server's
+`sentence_api/.env`):
+
+```kotlin
+const val ASSESSMENT_API_KEY = "replace-with-your-client-api-key"
+```
+
+The app requests microphone permission at runtime on first use.
+
+### Troubleshooting "云端暂不可用"
+
+That label means `GET /api/v1/videos` failed. Since the fix, the sample app
+shows the underlying error next to the label (for example DNS resolution,
+timeout, TLS, or an unexpected HTTP status). Common causes:
+
+- The APK was built with the wrong `SERVER_BASE_URL` for your deployment.
+- The phone cannot reach the domain/IP (check with a browser on the phone, and
+  verify the server with `curl https://<server>/api/v1/videos`).
+- The gateway only exposes plain HTTP, so the app must use `http://...` instead
+  of `https://...`.
+- The server certificate is invalid/self-signed on the phone; use HTTP for
+  internal testing or install a valid certificate at the gateway.
+
 ## Local Video Testing
 
 The computer path `/Users/...` is not visible to an Android device. For a