Reading MP3 information using objective c

I have mp3 files stored on the iPhone and I my application should to be able to read the 开发者_运维知识库ID3 information, i.e length in seconds, artist, etc. Does anyone know how to do this or what library to use in Objective-C?

Your thoughts are much appreciated.

ID3 information can be read retrieving the kAudioFilePropertyInfoDictionary property of an audio file using the AudioFileGetProperty function of the AudioToolbox framework.

A detailed explanation is available at iphonedevbook.com

edit: Original link is now down. InformIT has some similar sample code, but it's not as complete.

Look into the Media Player framework:

• Guide
• Reference
• All documentation

This requires that the MP3 in question is part of the iPod library on the phone.

For example, determining the name of every media file on the phone (including movies, podcasts, etc.):

MPMediaQuery *everything = [[MPMediaQuery alloc] init];

NSArray *itemsFromGenericQuery = [everything items];
for (MPMediaItem *item in itemsFromGenericQuery) {
    NSString *itemTitle = [item valueForProperty:MPMediaItemPropertyTitle];
    // ...
}

It appears that the following properties are available:

• MPMediaItemPropertyMediaType
• MPMediaItemPropertyTitle
• MPMediaItemPropertyAlbumTitle
• MPMediaItemPropertyArtist
• MPMediaItemPropertyAlbumArtist
• MPMediaItemPropertyGenre
• MPMediaItemPropertyComposer
• MPMediaItemPropertyPlaybackDuration
• MPMediaItemPropertyAlbumTrackNumber
• MPMediaItemPropertyAlbumTrackCount
• MPMediaItemPropertyDiscNumber
• MPMediaItemPropertyDiscCount
• MPMediaItemPropertyArtwork
• MPMediaItemPropertyLyrics
• MPMediaItemPropertyIsCompilation

Doing this without going through the media player framework will be somewhat difficult, and will need an external framework.

There are not many ID3 parsing libraries out there that are not GPLed. There is on Objective-C framework that could probably be modified to work on the iPhone when statically linked, but it is LGPL. In order to satisfy the terms of the LGPL with a statically linked binary you have to provide enough of the intermediary components that someone could relink it with their own version of the library, which is difficult (but not impossible) for an iPhone app. Of course since I have not been in a position where I have had to do that I have not actually discussed it with a lawyer, and since I am not one you should not take that as authoritative.

Your best bet if you don't feel like consulting a lawyer is to use a more liberally licensed C library like libID3 and wrap that in some Objective C classes. I would also recommend just directly including the code rather than dealing with all the static library build and link issues, but that is just a personal style thing.