How to detect if an MPMediaItem represents a DRM-protected audio track on iOS

Here’s how I do it:

MPMediaItem* item;

NSURL* assetURL = [item valueForProperty:MPMediaItemPropertyAssetURL];
NSString *title=[item valueForProperty:MPMediaItemPropertyTitle];

if (!assetURL) {
    /*
     * !!!: When MPMediaItemPropertyAssetURL is nil, it typically means the file
     * in question is protected by DRM. (old m4p files)
     */
    NSLog(@"%@ has DRM",title);
}