objective c - iOS AVFoundation: How do I fetch artwork from an mp3 file?

Question

My code:

- (void)metadata {
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:self.fileURL options:nil];

NSArray *artworks = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtwork keySpace:AVMetadataKeySpaceCommon];
NSArray *titles = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyTitle keySpace:AVMetadataKeySpaceCommon];
NSArray *artists = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtist keySpace:AVMetadataKeySpaceCommon];
NSArray *albumNames = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyAlbumName keySpace:AVMetadataKeySpaceCommon];

AVMetadataItem *artwork = [artworks objectAtIndex:0];
AVMetadataItem *title = [titles objectAtIndex:0];
AVMetadataItem *artist = [artists objectAtIndex:0];
AVMetadataItem *albumName = [albumNames objectAtIndex:0];

if ([artwork.keySpace isEqualToString:AVMetadataKeySpaceID3]) {
    NSDictionary *dictionary = [artwork.value copyWithZone:nil];
    self.currentSongArtwork = [UIImage imageWithData:[dictionary objectForKey:@"data"]];
}
else if ([artwork.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
    self.currentSongArtwork = [UIImage imageWithData:[artwork.value copyWithZone:nil]];
}

self.currentSongTitle = [title.value copyWithZone:nil];
self.currentSongArtist = [artist.value copyWithZone:nil];
self.currentSongAlbumName = [albumName.value copyWithZone:nil];
self.currentSongDuration = self.audioPlayer.duration;
}

This works for fetching artwork from m4a files, but doesn’t work for mp3 files. If the asset points to an mp3 file, artworks is empty. What am I doing wrong and how do I fix it?

Answer 1

I found that the artworks were being loaded asynchronously while the image was being set synchronously. I solved it this way:

- (void)metadata {
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:self.fileURL options:nil];

NSArray *titles = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyTitle keySpace:AVMetadataKeySpaceCommon];
NSArray *artists = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyArtist keySpace:AVMetadataKeySpaceCommon];
NSArray *albumNames = [AVMetadataItem metadataItemsFromArray:asset.commonMetadata withKey:AVMetadataCommonKeyAlbumName keySpace:AVMetadataKeySpaceCommon];

AVMetadataItem *title = [titles objectAtIndex:0];
AVMetadataItem *artist = [artists objectAtIndex:0];
AVMetadataItem *albumName = [albumNames objectAtIndex:0];


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 *d = [item.value copyWithZone:nil];
            self.currentSongArtwork = [UIImage imageWithData:[d objectForKey:@"data"]];
        } else if ([item.keySpace isEqualToString:AVMetadataKeySpaceiTunes]) {
            self.currentSongArtwork = [UIImage imageWithData:[item.value copyWithZone:nil]];
        }
    }
}];


self.currentSongTitle = [title.value copyWithZone:nil];
self.currentSongArtist = [artist.value copyWithZone:nil];
self.currentSongAlbumName = [albumName.value copyWithZone:nil];
self.currentSongDuration = self.audioPlayer.duration;
}