The pronunciation on the audio file is a casual, reduced style that develops naturally as one becomes more fluent in a language.  Reduction is not usually taught initially.  It is better for learners to learn a clearer pronunciation-- one that can be used, for instance, in public speaking.

Sorry-- offhand, no.  I happen to use a locally-produced, privately-published textbook myself.   Most pronunciation texts should have a section on reduction and liaison, however.  Googling 'pronunciation reduction' may lead you to some appropriate links.

Maybe it's not detailed enough, but I think this page could be a good starting point.

Hi Anon,
I'm interested in what you learned. Could you please me tell me your country? I think I'll open a tread entitled "English in your country: teaching and learning", sooner or later. I want to find out if it is only in Italy that English is taught in the worst way.

You are right, it's not really pronounced as you wrote (it's usually more like Marvin said), but in that clip is very very reduced. So now your question is:

Anonymous wrote:

if it is the case, why do we teach and learn /did yu evər/?

Because it depends on how English is taught and wheather your teachers are good or not. I think my teachers didn't really know what English was, but if they knew, they were not able to teach it. I always got very good grades when I was in high school, even though I didn't even know that "this" and "these" were pronounced differently.
As for that "Did you ever...", I learned it was wrong, we had to say "Have you ever...". Well, if you want to know how they teached me to pronounce "Did you", than your sentence would have been said: /did ju ɛvar juz e nidol/ (IPA) - /ai fiŋk dɛt's (h)au en italian tolks/

So where did I learn that "did you" could become /dɪdʒju/ or even /dʒʊ/? (it depends, that could vary a lot)
I realized that native speakers were spaking in a strange way, it seemed they didn't feel like pronouncing words correctly. Then I read a book on accent reduction, and I realized it was me who wasn't pronouncing words correctly.

The book is "American Accent Training" by Ann Cook. I think there are others, but I only tried that one, it's anyway among the best and very popular. I don't feel like commenting on that book now (I already did it in some other thread), but if you are interested, it's not a problem for me to give you some more info.

I hope I helped at least a little.