We released Mapping Tonal Harmony Pro 6 a few days ago.

One of the best features in the app is to be able to load and play tracks from the iPad’s Library. The process is pretty straight forward but we’ve encounter a few unexpected problems in the process.

We wanted the user to be able to pick a track from their library and load it into the app.
In order to do this the best option is to use the mediaPicker
This is how you call it:
– (void)chooseASongFromYourLibraryOnView:(UIViewController*) pViewController {
    MPMediaPickerController *picker =
    [[MPMediaPickerController alloc] initWithMediaTypes: MPMediaTypeMusic];
    
    picker.delegate                     = self;
    picker.allowsPickingMultipleItems   = NO;
    picker.prompt                       = NSLocalizedString (@”Select any song from the list”, @”Choose one song only”);
   
    curPickerController=picker;
    [pViewController presentViewController:picker animated:YES completion:nil];
}

Here’s the function called after the user has picked a track
– (void) mediaPicker: (MPMediaPickerController *) mediaPicker didPickMediaItems: (MPMediaItemCollection *) mediaItemCollection
{
    [myPlayer setQueueWithItemCollection:mediaItemCollection];
    NSArray *itemsFromGenericQuery = [mediaItemCollection items];
    self.pickedMediaItemSong=[itemsFromGenericQuery objectAtIndex:0];
    [curPickerController dismissViewControllerAnimated:NO completion:nil];

}

So, we saved the item in pickedMediaItemSong

To play and draw the wave-form representation of the track you need to get the song as a AVURLAsset

asset = [[AVURLAsset alloc] initWithURL:[self.pickedMediaItemSong valueForProperty:MPMediaItemPropertyAssetURL] options:nil];

But, the app would not play items from the cloud

Solution: filter the items shown by the mediapicker to non-cloud items only
add:     picker.showsCloudItems=NO; before you present the ViewController

Now, everything seemed to work fine for a while but every now and then the MPMediaItemPropertyAssetURL would retrun NULL (the asset would end up being nil). And it only happened with a few tracks in our library.

Why? Becuase those tracks had DRM!!

Here’s what Apple Says:

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