Any guidelines for handling the Headset and Bluetooth AVRC transport controls in Android 2.2

I am trying to figure out what is the correct (new) approach for handling the Intent.ACTION_MEDIA_BUTTON in Froyo. In pre 2.2 days we had to register a BroadcastReceiver (either permanently or at run-time) and the Media Button events would arrive, as long as no other application intercepts the开发者_如何学Cm and aborts the broadcast.

Froyo seems to still somewhat support that model (at least for the wired headset), but it also introduces the registerMediaButtonEventReceiver, and unregisterMediaButtonEventReceiver methods that seem to control the "transport focus" between applications.

During my experiments, using registerMediaButtonEventReceiver does cause both the bluetooth and the wired headset button presses to be routed to the application's broadcast receiver (the app gets the "transport focus"), but it looks like any change in the audio routing (for example unplugging the headset) shits the focus back to the default media player.

What is the logic behind the implementation in Android 2.2? What is correct way to handle transport controls? Do we have to detect the change in the audio routing and try to re-gain the focus?

This is an issue that any 3rd party media player on the Android platform has to deal with, so I hope that somebody (probably a Google Engineer) can provide some guidelines that we can all follow. Having a standard approach may make headset button controls a bit more predictable for the end users.

Stefan

Google has a detailed blog post on implementing the newer 2.2 AudioManager media button event receiver while maintaining backwards compatibility with older devices.

http://android-developers.blogspot.com/2010/06/allowing-applications-to-play-nicer.html

After some experiments, I was able to get a working solution with the new transport and audio focus infrastructure in Android 2.2.

What I end up doing is requesting both the Audio Focus (using AudioManager.requestAudioFocus) and the Trasport Focus (using AudioManagter.registerMediaButtonEventReceiver) every time my application starts playback.

requestAudioFocus takes a callback that is called when the audio focus is taken away from you (for example the internal player starts a playback). In my case I just pause the playback in my application if the focus is taken permanently. Same callback also now tells you that the focus is taken only temporary (for example the Nav system is talking) so you can "duck" your playback - lower the volume or pause and resume after it is done talking.

The only issue remaining is that the built in Music Player takes the transport focus every time you connect a Bluetooth headset. This has the effect where the first press of the Play button on the headset after connecting it, always starts the playback in the default Music Player.

There is probably a way to detect the headset connection and "hijack" the transport focus. In my case, I decided to not "fight" the default player, and get the transport focus back when the user manually starts the playback in my application.

If somebody has more insight or knows of a better way of handling the transport/audio focus, please share it.

I also have this same issue with the media button registration.

Periodically the Android returns the media button registration to the default music player. I have not been able to figure out why. This can happen while may application is actively playing as well as while my application playback is paused.

After a number of users complained that their Bluetooth pause and play control buttons would periodically stop working to control my application, I implemented code that re-registers my application by calling registerMediaButtonEventReceiver every 2 seconds. This allows me to get the button registration back and for the most part avoids the time window where where the user presses a Bluetooth media button and the default media player ends up responding.

My application is holding the audio focus during this entire time period, but still loses the Bluetooth button events periodically while it has audio focus. My application always unregisters the media button event receiver if it is called with a notification that it is losing the audio focus, and then registers again if it is later called when a temporary audio focus loss returns the audio focus.

The work around to keep the 2 second timer running and re-registering has been working, but I would like to get rid of this 2 second timer if someone has found a work around for the media button registration periodically switching back to the default media player.