Integrate webxdc WebView audio playback with Android media session

[Copilot]

Webxdc mini-apps playing audio have no Android system media notification, no background playback, and no hardware media key support. This adds full media session integration for webxdc audio — matching what Chrome/Firefox do for browser tab audio.

New: WebxdcMediaSessionService

A MediaSessionService backed by a stub SimpleBasePlayer (no ExoPlayer — the WebView owns the audio engine). The stub player exists solely to drive the system media notification and respond to play/pause from the notification or hardware keys.

• Accepts 4 custom SessionCommands from WebxdcActivity: WEBXDC_AUDIO_STARTED (+ title/artist/msgId for notification tap intent), WEBXDC_AUDIO_STOPPED, WEBXDC_AUDIO_PAUSED, WEBXDC_AUDIO_RESUMED
• Relays notification play/pause back to the activity via package-scoped broadcasts (ACTION_NOTIFICATION_PAUSE / ACTION_NOTIFICATION_RESUME)
• Updates SessionActivity PendingIntent per-instance so tapping the notification reopens the correct webxdc

Modified: WebxdcActivity

• Connects a MediaController to WebxdcMediaSessionService on onCreate; releases + sends AUDIO_STOPPED on onDestroy
• Registers BroadcastReceiver for notification pause/resume → evaluateJavascript to pause/play <audio>/<video> in the WebView
• Adds @JavascriptInterface methods (notifyAudioStarted, notifyAudioPaused, notifyAudioStopped, notifyAudioResumed) to InternalJSApi, all dispatched to main thread via Util.runOnMain
• Overrides pauseWebViewOnPause() → !isAudioPlaying to keep WebView JS timers and audio alive in the background

Modified: WebViewActivity

Adds pauseWebViewOnPause() hook (default true) so subclasses can suppress webView.onPause():

@Override
protected boolean pauseWebViewOnPause() {
    return !isAudioPlaying;
}

Modified: webxdc.js

Appended after the webxdc API setup — runs inside the iframe context where InternalJSApi is already accessible. Uses setInterval polling (2 s) to attach play/pause/ended listeners to <audio>/<video> elements including dynamically created ones:

el.addEventListener('play', function() {
  if (window.InternalJSApi) InternalJSApi.notifyAudioStarted(document.title || '');
});

Modified: AndroidManifest.xml

Registers WebxdcMediaSessionService with foregroundServiceType="mediaPlayback" alongside the existing AudioPlaybackService. Existing voice message playback is untouched.

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Original prompt

Feature: Integrate Webxdc WebView audio playback with Android media session

When a webxdc mini-app plays music/audio, it should integrate with the Android system media notification (like how Chrome/Firefox browsers do on Android when media is playing in a tab), and the webxdc activity should be allowed to keep running in the background while audio is playing.

How it works in browsers (reference behavior)

When a browser tab plays audio, Android:

1. Shows a media notification with play/pause controls
2. Allows the audio to keep playing when the user navigates away (background)
3. Responds to hardware media keys (play/pause, next, previous)
4. Stops playback when another app requests audio focus

Existing infrastructure

The app already has AudioPlaybackService (src/main/java/org/thoughtcrime/securesms/service/AudioPlaybackService.java) — a MediaSessionService backed by ExoPlayer + MediaSession (androidx.media3) — used for voice message playback. The manifest already declares FOREGROUND_SERVICE_MEDIA_PLAYBACK permission and registers AudioPlaybackService.

What needs to be implemented

The approach is to create a new dedicated WebxdcMediaSessionService (modeled after AudioPlaybackService) that uses a MediaSession with no ExoPlayer (the actual audio is played by the WebView's internal audio engine, not ExoPlayer). Instead it uses MediaSession purely to:

• Post the system media notification (managed automatically by MediaSessionService)
• Register Player.Listener / MediaSession.Callback so the notification's play/pause button works (by calling back into the WebView via JS)
• Keep the process alive in the foreground while audio is playing

Files to create

src/main/java/org/thoughtcrime/securesms/service/WebxdcMediaSessionService.java

A new MediaSessionService that:

• Holds a MediaSession wrapping a stub Player (a ForwardingSimpleBasePlayer or a minimal SimpleBasePlayer subclass from androidx.media3 that reports STATE_READY/STATE_IDLE and playWhenReady).
  • Use androidx.media3.common.SimpleBasePlayer (available in media3 1.x): override getState() to report the current playback state, and handleSetPlayWhenReady()/handleStop() to relay commands back to WebxdcActivity via a broadcast or a bound service interface.
• Exposes custom SessionCommands:
  • "WEBXDC_AUDIO_STARTED" (args: title, artist/app-name, optional artwork as byte[]) — called by WebxdcActivity when the WebView reports audio playing; updates the MediaMetadata on the session and puts the service into foreground (starts it).
  • "WEBXDC_AUDIO_STOPPED" — called by WebxdcActivity when audio stops; removes the notification and stops the foreground service.
  • "WEBXDC_AUDIO_PAUSED" — updates player state to paused.
  • "WEBXDC_AUDIO_RESUMED" — updates player state to playing.
• The stub player's handleSetPlayWhenReady(false) (user pressed pause in notification) should send a local broadcast or callback that WebxdcActivity listens to, calling webView.evaluateJavascript(...) to pause the WebView audio (e.g. document.querySelectorAll('audio,video').forEach(el => el.pause())).
• The stub player's handleSetPlayWhenReady(true) should resume playback in the WebView similarly.
• Sets sessionActivity PendingIntent to reopen the WebxdcActivity (the activity provides msgId, accountId extras via "WEBXDC_AUDIO_STARTED").
• Registers the service in the manifest with foregroundServiceType="mediaPlayback" and an androidx.media3.session.MediaSessionService intent-filter.

Files to modify

src/main/java/org/thoughtcrime/securesms/WebxdcActivity.java

1. Detect WebView audio state using WebChromeClient.onCreateWindow / overriding WebChromeClient with audio focus detection. The cleanest approach for WebView audio detection is:

   • Add a @JavascriptInterface method notifyAudioStarted(String title) and notifyAudioStopped() to InternalJSApi.
   • Inject a small script into webxdc.js or via evaluateJavascript on page load that attaches play/pause/ended event listeners to all <audio> and <video> elements (including dynamically created ones via a MutationObserver), and calls InternalJSApi.notifyAudioStarted(document.title) / notifyAudioStopped().
   • Inject this script after page load in WebChromeClient.onPageFinished equivalent — use webView.addJavascriptInterface already done, and call evaluateJavascript from WebViewClient.onPageFinished (override in WebxdcActivity's WebChromeClient setup).

2. Connect to WebxdcMediaSessionService using MediaController (like ConversationActivity does with AudioPlaybackService):

   • In onCreate: build a MediaController against WebxdcMediaSessionService's SessionToken.
   • In onDestroy: release the MediaController and send WEBXDC_AUDIO_STOPPED.

3. Send commands from JS callbacks:

   • notifyAudioStarted(title): sen...

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