Extracting MP3 Album artwork in iOS - iphone

Question

I have been trying to extract metadata information from a .mp3 file for an iPhone app. I tried using AVAsset like this.It didn't work,the common meta data is empty. But audacity and another iOS app from app store could retrieve the meta data details. I don't know why?.
So, I tried to extract the same with below code using AudioToolBox framework
CFDictionaryRef piDict = nil;
UInt32 piDataSize = sizeof(piDict);
// Populates a CFDictionary with the ID3 tag properties
err = AudioFileGetProperty(fileID, kAudioFilePropertyInfoDictionary, &piDataSize, &piDict);
if(err != noErr) {
NSLog(#"AudioFileGetProperty failed for property info dictionary");
return nil;
}
// Toll free bridge the CFDictionary so that we can interact with it via objc
NSMutableDictionary* nsDict = [(__bridge NSDictionary*)piDict mutableCopy];
This returned everything except album art. When I tried to extract the album art using kAudioFilePropertyAlbumArtwork , I got osstatus error(The operation couldn't be completed).
So at last, I tried my luck with ObjC wrapper for libId3(found here). It worked perfectly well. I could get the artwork.
My question is, why AVAsset could not retrieve the data?. What am I missing there?. somebody managed to to get it work?. A sample will be appreciated.
Why kAudioFilePropertyAlbumArtwork extraction couldn't be completed?. Both the issues happened with all the .mp3 files I had.
Solution Update:
AVAsset didn't work for me because I made my URL using
[NSURL URLWithString:[filePath stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]
rather than
NSURL *fileURL = [NSURL fileURLWithPath:filePath];

Answer 1

To use AVAsset to extract metadata informations, this post is useful. The following code is what you need:
NSString *filePath = [[NSBundle mainBundle] pathForResource:#"filename" ofType:#"mp3"];
NSURL *fileURL = [NSURL fileURLWithPath:filePath];
AVAsset *asset = [AVURLAsset URLAssetWithURL:fileURL options:nil];
NSArray *keys = [NSArray arrayWithObjects:#"commonMetadata", nil];
[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^{
NSArray *artworks = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata
withKey:AVMetadataCommonKeyArtwork
keySpace:AVMetadataKeySpaceCommon];
for (AVMetadataItem *item in artworks) {
if ([item.keySpace isEqualToString:AVMetadataKeySpaceID3]) {
NSDictionary *dict = [item.value copyWithZone:nil];
self.imageView.image = [UIImage imageWithData:[dict objectForKey:#"data"]];
} else if ([item.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
self.imageView.image = [UIImage imageWithData:[item.value copyWithZone:nil]];
}
}
}];

Answer 2

NSURL *fileURL1 = [NSURL fileURLWithPath:url];
AVAsset *asset = [AVAsset assetWithURL:fileURL1];
for (AVMetadataItem *metadataItem in asset.commonMetadata) {
if ([metadataItem.commonKey isEqualToString:#"artwork"]){
NSDictionary *imageDataDictionary = (NSDictionary *)metadataItem.value;
NSData *imageData = [imageDataDictionary objectForKey:#"data"];
UIImage *image = [UIImage imageWithData:imageData];
imageThumb.image = image;
}
}