fix(tts): add missing supported timeline command to TtsSessionAdapter

[ddfreiling]

without this command the session-adapter didn't properly report the current timeline to a media3.MediaSession

[qnga]

What is timeline used for?

[ddfreiling]

If using the ForwardingSimpleBasePlayer to modify MediaSession, it has a getState function to build the player state, which depends on the adapter player allowing the COMMAND_GET_TIMELINE to be called, which currently TtsSessionAdapter does not.

[qnga]

I understand that. But what does this getState do better with the timeline? I'm not entirely sure my timeline implementation is good or useful in the adapter, that's why I ask.

[ddfreiling]

Without a timeline the SimpleBasePlayer dies on an assert that timeline must not be empty if the player is not in IDLE state. For us this crashes the entire MediaSession when we call openSession on it with a TtsNavigator.

Exception:

SimpleBasePlayer: Empty playlist only allowed in STATE_IDLE or STATE_ENDED

As long as SimpleBasePlayer sees a non-empty timeline, everything seems to work.

I guess this only happens, since we wrap the navigator.asMedia3Player() in a ForwardingSimpleBasePlayer to better control certain media-button events and notification button layout. Maybe there's another way to do this?

[qnga]

Ok, I see. If you want a specific notification button layout, you might expect a better timeline than my shitty one. Are you expecting resource-based navigation in the notification? I might have not exposed it because of the notification actually, I need to check.

[qnga]

As far as I understand and remember the missing timeline command is more of a feature than a bug. To prevent your crash you should be able to provide a timeline by yourself by overriding getState or something of that ilk. If for some some reason that's not enough, please report your use case in detail.

[ddfreiling]

@qnga turns out I have to completely duplicate/re-implement the entire getState method of ForwardingSimpleBasePlayer. Because if I call super.state and just expand on that, I still get the assert exception:

Empty playlist only allowed in STATE_IDLE or STATE_ENDED

So basically I have to copy their implementation but leave out this non-empty playlist assert and the check on AvailableCommands.COMMAND_GET_TIMELINE.

Maybe the TtsSessionAdapter should just report a single item on the playlist when active?

[qnga]

A single-item timeline sounds reasonable. As mentioned above, my main concern is about the notification. Any solution not making the backward and forward buttons appear in the default notification would be fine with me as this was the intended behavior.

[ddfreiling]

What do you think about this solution? In the test-app I'm seeing a simple notification with just a pause/play button now, which also supports wrapping the player in a ForwardingSimpleBasePlayer.