If a user downloads the podcast episode using the podcasts app, a lot of the metadata is lost(comments etc). If the user gets the podcast on the device by using iTunes sync, most of the data is there. I've meant to file a bug but haven't. One way to get at some data that might not show up using the MPMediaPlayer framework is to use AVFoundation to get the id3 tag data directly.
#import <AVFoundation/AVFoundation.h>
#import <MediaPlayer/MediaPlayer.h>
MPMediaItem *item;
AVURLAsset *itemAsset = [item valueForProperty:MPMediaItemPropertyAssetURL];
NSArray *mDatsForFormats = [itemAsset metadataForFormat:@"org.id3"];
for (AVMetadataItem *mDatItem in mDatsForFormats){
if (mDatItem.stringValue) {
NSLog(@"\nkey %@\nvalue %@",mDatItem.key,mDatItem.stringValue);
}
NSLog(@"%@",mDatItem);
}