Or how to convert an MPMediaItem into an NSDictionary ?
That’s pretty easy :

MPMediaItem contains values targetable through the following properties :

MPMediaItemPropertyAlbumArtist
MPMediaItemPropertyAlbumArtistPersistentID
MPMediaItemPropertyAlbumPersistentID
MPMediaItemPropertyAlbumTitle
MPMediaItemPropertyAlbumTrackCount
MPMediaItemPropertyAlbumTrackNumber
MPMediaItemPropertyArtist
MPMediaItemPropertyArtistPersistentID
MPMediaItemPropertyArtwork
MPMediaItemPropertyAssetURL
MPMediaItemPropertyBeatsPerMinute
MPMediaItemPropertyComments
MPMediaItemPropertyComposer
MPMediaItemPropertyComposerPersistentID
MPMediaItemPropertyDiscCount
MPMediaItemPropertyDiscNumber
MPMediaItemPropertyGenre
MPMediaItemPropertyGenrePersistentID
MPMediaItemPropertyIsCloudItem
MPMediaItemPropertyIsCompilation
MPMediaItemPropertyLyrics
MPMediaItemPropertyMediaType
MPMediaItemPropertyPersistentID
MPMediaItemPropertyPlaybackDuration
MPMediaItemPropertyPodcastPersistentID
MPMediaItemPropertyReleaseDate

So you can easily write the code to convert everything, taking care of not including nil values :

- (NSDictionary *)fastEnumarateMPMedia:(MPMediaItem *)media {
    NSMutableDictionary *dico = 
[[NSMutableDictionary alloc] init];
    if ([media valueForProperty: MPMediaItemPropertyAlbumArtist]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumArtist] forKey:@"MPMediaItemPropertyAlbumArtist"];
    if ([media valueForProperty: MPMediaItemPropertyAlbumArtistPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumArtistPersistentID] forKey:@"MPMediaItemPropertyAlbumArtistPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyAlbumPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumPersistentID] forKey:@"MPMediaItemPropertyAlbumPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyAlbumTitle]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumTitle] forKey:@"MPMediaItemPropertyAlbumTitle"];
    if ([media valueForProperty: MPMediaItemPropertyAlbumTrackCount]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumTrackCount] forKey:@"MPMediaItemPropertyAlbumTrackCount"];
    if ([media valueForProperty: MPMediaItemPropertyAlbumTrackNumber]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAlbumTrackNumber] forKey:@"MPMediaItemPropertyAlbumTrackNumber"];
    if ([media valueForProperty: MPMediaItemPropertyArtist]) [dico setObject:[media valueForProperty: MPMediaItemPropertyArtist] forKey:@"MPMediaItemPropertyArtist"];
    if ([media valueForProperty: MPMediaItemPropertyArtistPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyArtistPersistentID] forKey:@"MPMediaItemPropertyArtistPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyArtwork]) [dico setObject:[media valueForProperty: MPMediaItemPropertyArtwork] forKey:@"MPMediaItemPropertyArtwork"];
    if ([media valueForProperty: MPMediaItemPropertyAssetURL]) [dico setObject:[media valueForProperty: MPMediaItemPropertyAssetURL] forKey:@"MPMediaItemPropertyAssetURL"];
    if ([media valueForProperty: MPMediaItemPropertyBeatsPerMinute]) [dico setObject:[media valueForProperty: MPMediaItemPropertyBeatsPerMinute] forKey:@"MPMediaItemPropertyBeatsPerMinute"];
    if ([media valueForProperty: MPMediaItemPropertyComments]) [dico setObject:[media valueForProperty: MPMediaItemPropertyComments] forKey:@"MPMediaItemPropertyComments"];
    if ([media valueForProperty: MPMediaItemPropertyComposer]) [dico setObject:[media valueForProperty: MPMediaItemPropertyComposer] forKey:@"MPMediaItemPropertyComposer"];
    if ([media valueForProperty: MPMediaItemPropertyComposerPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyComposerPersistentID] forKey:@"MPMediaItemPropertyComposerPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyDiscCount]) [dico setObject:[media valueForProperty: MPMediaItemPropertyDiscCount] forKey:@"MPMediaItemPropertyDiscCount"];
    if ([media valueForProperty: MPMediaItemPropertyDiscNumber]) [dico setObject:[media valueForProperty: MPMediaItemPropertyDiscNumber] forKey:@"MPMediaItemPropertyDiscNumber"];
    if ([media valueForProperty: MPMediaItemPropertyGenre]) [dico setObject:[media valueForProperty: MPMediaItemPropertyGenre] forKey:@"MPMediaItemPropertyGenre"];
    if ([media valueForProperty: MPMediaItemPropertyGenrePersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyGenrePersistentID] forKey:@"MPMediaItemPropertyGenrePersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyIsCloudItem]) [dico setObject:[media valueForProperty: MPMediaItemPropertyIsCloudItem] forKey:@"MPMediaItemPropertyIsCloudItem"];
    if ([media valueForProperty: MPMediaItemPropertyIsCompilation]) [dico setObject:[media valueForProperty: MPMediaItemPropertyIsCompilation] forKey:@"MPMediaItemPropertyIsCompilation"];
    if ([media valueForProperty: MPMediaItemPropertyLyrics]) [dico setObject:[media valueForProperty: MPMediaItemPropertyLyrics] forKey:@"MPMediaItemPropertyLyrics"];
    if ([media valueForProperty: MPMediaItemPropertyMediaType]) [dico setObject:[media valueForProperty: MPMediaItemPropertyMediaType] forKey:@"MPMediaItemPropertyMediaType"];
    if ([media valueForProperty: MPMediaItemPropertyPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyPersistentID] forKey:@"MPMediaItemPropertyPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyPlaybackDuration]) [dico setObject:[media valueForProperty: MPMediaItemPropertyPlaybackDuration] forKey:@"MPMediaItemPropertyPlaybackDuration"];
    if ([media valueForProperty: MPMediaItemPropertyPodcastPersistentID]) [dico setObject:[media valueForProperty: MPMediaItemPropertyPodcastPersistentID] forKey:@"MPMediaItemPropertyPodcastPersistentID"];
    if ([media valueForProperty: MPMediaItemPropertyReleaseDate]) [dico setObject:[media valueForProperty: MPMediaItemPropertyReleaseDate] forKey:@"MPMediaItemPropertyReleaseDate"];
    return dico;
}