Support media resumption with session demo app

[spun]

To support the "Media Resumption" feature introduced in Android 11, we need to "implement a MediaSession callback for onPlay()".

With media3, the MediaLibrarySessionCallback is replacing onPrepareFromMediaId, onPrepareFromSearch, onPrepareFromUri, onPlayFromMediaId, onPlayFromSearch, onPlayFromUri with onSetMediaUri, but the simple onPlay with no input is not included and I can't find an easy way to implement it.

Edit: Is not included in the documentation, but the "Media Resumption" feature is also calling onPrepare() and, after reading through MediaSessionLegacyStub, I was able to "fake" an onPrepare() by catching COMMAND_PREPARE (only dispatched inside onPrepare with no input). I couldn't do the same to fake the onPlay since it uses the COMMAND_PLAY_PAUSE and that command could mean onPlay or onPause, but the onPrepare replacement seems to be enough to support the feature for now.

[marcbaechinger]

I understand that media resumption is still using a legacy MediaControllerCompat to talk to your media session. If this is the case then the system would use something like mediaController.getTransportControls().play() to send the play request.

This corresponds to the documentation of MediaSession.Callback.onPlay() saying: Override to handle requests to begin playback..

If this is the case I would expect that such a legacy call needs to be delegated to the Media3 MediaSession that then would call player.play() or player.setPlayWhenReady(true) on the player with which the media session has been built. I expect that this backwards compatibility is provided by the MediaSessionService (of which the MediaLibraryService is a subclass). If this is not the case this would qualified to be labeled as a bug rather than we need to add a method to the session callback.

Can you clarify whether you found that player.play() or player.setPlayWhenReady(true) is not called when media resumption happens?

[spun]

The play() in player is called correctly, my problem is more about the need to override onPlay() to support the feature. Let me list the calls that "Media Resumption" makes to try to explain what I mean better.

Media Resumption Steps (source)

1. System calls onGetRoot/onGetLibraryRoot with EXTRA_RECENT hint
2. The app returns the root of a media tree that contains the recently played media
3. System calls onLoadChildren/onGetChildren with the Root from step 2 as parentId
4. The app returns the recently played MediaItem

Note: At this point, the system shows the static placeholder notification with the play button. If the user taps on the play button:

6. System calls onGetRoot/onGetLibraryRoot with EXTRA_RECENT hint again
7. System connects to MediaSession and issues a play command to it.

---

At first I thought that the System play call (step 7) would include the mediaId from step 4 and I could use the media3 equivalent to MediaSession.onPlayFromMediaId, but it doesn't, it just issues the play command.

After reading the documentation and the UAMP implementation (I've checked the playWhenReady value and is always true, UAMP doesn't have ACTION_PREPARE as supported action), my assumption was that the System expects that, when the play command is issued (step 7), the app MediaSession.onPlay() will:

• Check that nothing is playing right now (UAMP has this check for free, since it's using the MediaSessionConnector from exoplayer)
• Get the last media played (db, preferences, etc)
• Create a MediaItem
• Prepare it
• Play it

Sorry if it's still not clear. My main doubt was to know where should I retrieve and prepare the MediaItem. The docs mention onPlay() and UAMP seems to do it inside its onPlay() equivalent. That's why I was looking for a direct replacement but maybe there is a better solution that I'm no seeing.

[marcbaechinger]

Thanks for the detailed answer! I think best is to add media resumption to the session demo app (see docs). I renamed the issue accordingly and it's kept as an enhancement. I'm not sure when we get around to do that yet I'm afraid

I can confirm the protocol you are describing with the 3 calls from systemui to the service and the play() command at the end.

MediaSessionCompat.Callback.onPlay is in Media3 Player.play() or Player.setPlayWhenReady(true).

The first two calls to the service are used to created the notification. The service is not started by intent, and when systemui unbinds the service is stopped.

Then after potentially a longer duration the user finds the notification and taps play. Now systemui calls the service again to start the service and call getLibraryRoot with the intention to prepare for playback. The service can load the most recent song again, set the media item and prepare and await 'play()'.

The service can recognize that systemui is the caller by its package name and also gets the isRecent flag to know to prepare the player.

[PaulWoitaschek]

I can't get this working at all and the notification is always unresponsive on Android 13.

Pocketcasts added a workaround here:
Automattic/pocket-casts-android@ead4b0c

Maybe that's a fix that can / should be incorporated into media3? @marcbaechinger

@ashiagr did you investigate into a proper solution after your temporary fix?

[marcbaechinger]

Pocketcasts added a workaround here:

I'm not sure how this is related. As far as I can see the code there is using the legacy androidx.media API.

I meant this works with UAMP in the media3 branch after I implemented it. I can test again when I have some cycles.

[ashiagr]

Hey @PaulWoitaschek 👋

I wasn't able to investigate a proper solution yet.

I upgraded ExoPlayer media library to 2.18.2 which corresponds to Media3 1.0.0-beta03 release but it didn't help.

As a workaround, I used legacy flags with stopForeground(...) that improved notifications responsiveness but it might have introduced side effects.

[PaulWoitaschek]

You are correct @marcbaechinger , with uamp it's working. I'll investigate more, thanks 🙏

If someone else is trying this out, here is a patch to update to rc1
m3.patch

[PaulWoitaschek]

I found the issue! And possibly also a better fix for pocket casts.

The main difference between my implementation and the one of the media3 uamp branch is that I don't have that onTaskRemoved stopSelf implementation.

This was causing a dead notification which is hanging. When clicking on the play button in logcat you can see a DeadObjectException.

To reproduce it, remove these lines in onTaskRemoved:

        releaseMediaSession()
        stopSelf()

• Then start playback in uamp.
• Pause it
• Go to the home screen
• Swipe away the app from the recents
• Now the notfication is dead and seems half broken (only a progressbar without time)

Additionally a fix for pocketcasts might be to call stopSelf from onTaskRemoved

[ashiagr]

a fix for pocketcasts might be to call stopSelf from onTaskRemoved

Already tried this @PaulWoitaschek, it doesn't seem to be working for us. Thanks so much for taking a look. 🙏 @marcbaechinger, is there anything you can suggest or things we should be checking to make it work with ExoPlayer's latest version?