Well, I just read through the whole 2 pages and ended up with a headache, but fair play to yourself, Nigel and Yvan. Tenacious seems like an understatement.
In a somewhat unrelated way, regardless of choosing between mdls and NSMetadataQuery, I've been using Apple's AVCaptureMovieFileOutput class in my latest app and have become frustated by why AVMetadataItem sometimes posts a duration for the video and sometimes doesn't. I'm beginning to think that whole AV framework is a bug-ridden nightmare.
Sorry, not really relevant. Just venting!