[A-EDev]

Summary

• Captions are fetched over Android's own Cronet (Media3 HttpEngineDataSource on android.net.http.HttpEngine) on Android 14 and newer. YouTube answers an auto-translated caption (&tlang=) over it and refuses the same URL over OkHttp with 429.
• Caption requests send only a Chrome mobile user agent and Accept, without the browser Origin, Referer and Sec-Fetch-* headers, like NewTube.
• A translation is made from the video's speech (ASR) track in VTT, skipping dubbed and timing-optimized tracks, like YouTube's apps.
• Each translated caption fetch is logged as loaded or refused, with its source track.

On a phone (same network, same video, interleaved runs), OkHttp got 429 on every translated request, while HttpEngineDataSource loaded the Arabic translation in 3 of 3 rounds, with the captions on screen.

Related issue

Part of #1369 and #1434

Change type

• Bug fix
• Feature
• Refactor or maintenance
• Build, packaging, or CI
• Documentation

Validation

• ./gradlew :app:assembleGithubDebug
• ./gradlew :app:testGithubDebugUnitTest --tests '*GoogleVideoRequestPolicyTest' --tests '*CaptionTrackResolverTest' --tests '*SubtitleLoadDiagnosticsTest' (22 tests, 0 failed)
• I ran any additional flavor-specific build or test tasks affected by this change. (spotlessCheck, :app:compileFossDebugKotlin, :app:lintGithubDebug)
• I manually tested the affected behavior on an Android device or emulator. Arabic (translated) on an English video: loaded over the platform engine (Cronet version: 150.0.7871.41, HttpEngineDataSource) after two 429 retries, fmt=vtt source=asr bytes=221001, Arabic captions on screen.

Test device and Android version: Xiaomi phone, Android 16 (API 36)

Screenshots or recordings

Risk and compatibility

• No new dependency: HttpEngineDataSource ships in media3-datasource 1.11.0 and the engine is part of Android 14.

• The engine is built once, on the first caption, and kept for the process.

• With the app proxy on, captions stay on OkHttp, since HttpEngine takes no proxy. Android 13 and older also stay on OkHttp.

• The change does not introduce secrets, private data, or unexpected telemetry.

• New user-facing text uses Android string resources.

• Dependency and lockfile changes are intentional and limited to this PR.

• Room schema changes include the required version bump and migration, or this PR does not change the Room schema.

• Breaking changes and upgrade steps are clearly documented.

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