Background Audio and Remote Control Support using MPMusicPlayerController on iOS 4. Is this even possible?

Question

I've spent two days on this and have gotten nowhere. I'm trying to use [MPMusicPlayerController applicationMusicPlayer] to play audio chosen from the user's iPod library and have it run in the background as well as support remote events. Now getting the music actually playing is the easy part. Get the instance, pick the songs, assign the music queue and play. Done and done. BUT... a) I can't get it to play in the background, and b) even when in the foreground I can't get the remote control events to work at all!

And before you ask, yes, I have set the plist entries, the audio session category, the call to say I'm interested in getting remote events and set up a first responder to listen for them, so please know, yes, I've read read every single document on the subject that I could find* (*a task I blame Apple for for not being clear at all on this topic, nor having ANY example code for it!) and I've watched every one of the WWDC videos relating to it (even freezing the screen to copy the code exactly from their example...) so unless I've missed something not in this list, replying with any of those answers is not going to help.

One more thing... I am explicitly talking about using the MPMusicPlayerController which according to the docs, never uses an application session. It always uses the system session. (Maybe that in itself answers my question, but the docs don't clearly say that so I'm not sure, hence this question.)

That said, after two days, my thoughts are this:

1. When using the MPMusicPlayerController, regardless of what methods you call or what plist entries you set, your app will never run in the background. Period. If you use the ipodMusicPlayer instance, the music keeps playing, but that's because it's the iPod that's playing, not your app. If you use the applicationMusicPlayer instance instead, when going to the background your music stops. In both cases, your app is suspended.

2. Regardless of your using the ipodMusicPlayer or applicationMusicPlayer instances, all remote events go to the iPod application itself, not yours, even if you've explicitly asked for them. If you are using the applicationMusicPlayer instance and you use the remote to select 'Play', the iPod app receives the command so your audio ducks out and is interrupted and playback begins in the iPod app. If you've chosen the ipodMusicPlayer instead, then of course it doesn't matter as you have explicitly said you're basically just interested in remotely controlling the iPod app which again, is what actually receives the remote events.

3. The icon in the quick-switch controls at the bottom never changes to your app's icon because again, your app is never actually set up to receive the events. The iPod application is, which is why its icon does appear there.

So what I want to know is... am I wrong here? Has anyone successfully been able to use MPMusicPlayerController and been able to intercept the remote events? While I'd prefer to use the applicationMusicPlayer with background music support so I don't muck with the user's iPod, the bigger thing is remote control notifications, meaning if I have to use the ipodMusicControl and keep my app in the foreground to intercept those messages, so be it. It's ugly that way, but at least it's something.

Code examples, or at least explicit steps against one of the built-in app templates would be GREATLY appreciated. (Don't even need the implementation... just the steps. Hopefully that will appease the inevitable 'It's still under NDA' thing that people keep answering questions with.)

Mark

Shortcoming

Answer 1

I solved it. The info is in my other question over here...

Stack Overflow: Play iPod music while receiving remote control events

...but the short version is you have to use AVPlayer (but not AVAudioPlayer. No idea why that is!) with the asset URL from the MPMediaItem you got from the library, then set the audio session's category to Playable (do NOT enable mixable!) and add the appropriate keys to your info.plist file telling the OS your app wants to support background audio.

This lets you play items from your iPod library (except Audible.com files for some reason!) and still get remote events. Granted you have to do more work, and since this is your audio player which is separate from, and will interrupt the iPod app (which may or may not be desirable. And again, don't enable mixing or the iPod app will hijack the remote control events) but those are the breaks!

Shortcoming

No problem. Really frustrating that Apple wasn't more clear about what was going on there. Even more frustrating (although understandable for DRM reasons) is that you can't do Audible files this way, which ruined our app since that was the main focus. What can ya do! Still, glad this helped. – Shortcoming

Answer 2

For anyone who wants to know, I found out to get the audio playing in the background, you have to set the audio session's category to Playable and then background audio works just fine. If you also want to play your own sounds at the same time, you have to mark the category as mixable. That solved the background music part. But what I've found out is any time the iPod is playing, it doesn't seem possible for you to get remote notifications.

Here's the updated thread...

How can you play music from the iPod app while still receiving remote control events in your app?

M

Shortcoming

How is this guy doing it??? Ugh!!! engadget.com/2010/07/08/… – Shortcoming

Hi, how do you record audio in the background? – Unapt