How can I find out all audio files whose formats are supported by AVAudioPlayer in Lion 10.7?

Question

I want to use codes like this.

NSMetadataQuery *query = [[NSMetadataQuery alloc] init];
[query setSearchScopes: [NSArray arrayWithObject: [NSURL fileURLWithPath:@"/Users/Someone/Music" isDirectory:YES]]];
[query setPredicate: predicate];
...
...

Now how do I suppose to set "predicate" to filter out those files with unsupported format??

kMDItemCodezs,kMDItemMediaTypes,kMDItemContentType,kMDItemKind?

Which one should I use? And what are all the possible values of these attibutes corresponding to the supported format in AVAudioPlayer in Lion 10.7? Thanks a lot.

Answer 1

To obtain a list of most supported formats, you can use AudioFileGetGlobalInfo in the AudioToolbox framework to get the UTIs supported by Core Audio (using kAudioFileGlobalInfo_AllUTIs):

UInt32 size;
NSArray *all;
OSStatus err;

err = AudioFileGetGlobalInfoSize(kAudioFileGlobalInfo_AllUTIs, 0, NULL, &size);
if (err == noErr)
    err = AudioFileGetGlobalInfo(kAudioFileGlobalInfo_AllUTIs, 0, NULL, &size, &all);
if (err == noErr)
    NSLog(@"UTIs: %@", all);
[all release];

On 10.7, this gives me:

"public.aiff-audio",
"public.ulaw-audio",
"org.3gpp.adaptive-multi-rate-audio",
"com.microsoft.waveform-audio",
"public.3gpp2",
"com.apple.coreaudio-format",
"public.3gpp",
"public.mp3",
"public.au-audio",
"public.mpeg-4-audio",
"public.mpeg-4",
"com.apple.m4a-audio",
"public.aifc-audio"

Unfortunately UTIs aren't defined for some of the more obscure data formats (e.g. .mp1/.mp2) Core Audio supports; if you're happy with the above subset, then just use the UTIs.

Then turn those into a NSMetadataQuery (kMDItemContentType for kAudioFileGlobalInfo_AllUTIs). If you want to cover the rest of the formats, you can match by HFS type and extension: kMDItemFSTypeCode for kAudioFileGlobalInfo_AllHFSTypeCodes, and a wildcard match of kMDItemFSName for kAudioFileGlobalInfo_AllExtensions. You can use afconvert -hf to display both of these.

Matching with NSMetadataQuery will of course not look inside all of the files, so it'll still find text files renamed with a .mp3 extension. Since Spotlight does try to index other audio attributes, you could try checking kMDItemAudioBitRate and so forth; these will be missing on a file that isn't actually an audio file. Depending on how accurate you want to be in filtering, you can also try opening each file to see if it's playable.

Answer 2

Use kMDItemContentTypeTree, and the audio type. This will match any audio files, ignoring movie files. If you want to include movie files, search for the audio-visual content type, which the audio type conforms to (descends from).

Edit: This will match all known audio types, regardless of whether Core Audio (let alone AVAudioPlayer) can play them. Nicholas Riley's solution is better.