Playback Resumption with external applications

[PaulWoitaschek]

On my audiobook player I received this PR which would cause all onConnect commands which do not come from my package to prepare the last played book.

PaulWoitaschek/Voice#2280

Previously it was already a little hacky because onGetSessionwas invoking the isReleased using reflection, see #422

I wonder if the proposed PR is really the intended solution with media3 to support playback resumption coming from external applications.
Could you give some guideance (and even better: Write some documentation) how this is designed to work?

[ASGusev]

I created the PR mentioned above. I tried to use the SimpleWear's media controller with Voice: I connected to Voice from the SimpleWear and hit the play button expecting Voice to continue playing the last played media like most other apps do, but it didn't. So, I looked at Voice's code and saw the onConnect loading the playback position if the connecting controller has Android Auto's package id. I relaxed the package id check to load position for all package ids but Voice's own. Then, the playback would resume from the last position on SimpleWear's play button but if the app was swiped away from the app drawer after being started by SimpleWear, it could end up in a state when the process was alive but the session was already released which meant that the app wasn't able to run playback even from it's main UI until being forcefully stopped, so I made onGetSession create a new session if the old one has been released

[marcbaechinger]

An external controller can connect to the session and then use the setMediaItems method to set items to the player and then call play. The app owning the controller must be in the foregropund for that to work on all API levels.

If the controller calls play when the playlist is empty, then I'd expect that onPlaybackResumption is called to fill the playlist with what is returned from the callback. That works with the demo app. Can you check why that doesn't work for your app? You can basically put a break point into handleMediaControllerPlayRequest to see what happens there.

That's the intended API Media3 offers. For a controller this would just be to build the controller and then call play:

controller.play()

I have verified this with the demo app:

1. Uncomment these lines in PlaybableForderActivivty
2. Add the lines

if (controller.mediaItemCount == 0) {
  controller.play()
}

at the end of PlayerActivity.setController.

With the above changes in the demo app, the PlayerActivity calls play on an empty controller which triggers playback resumption.

The mentioned PR does changes in the app logic that aren't specific to Media3 APIs, so the best person to review that change is the app developer I think.