In this 2009 lecture (posted in four parts), MacIntyre describes the progress of his thinking on moral philosophy.
Watch on YouTube.
He started as a Thomist, i.e. a Catholic Aristotelian, briefly embraced verificationism (well, he admired Ayer, in any case), and was frustrated with the number of seemingly permanent disagreements within both philosophy and politics/culture generally. He describes Sartre as a primary reaction point for the thought that eventually led to After Virtue; Sartre's existentialism stated that reasons for action were ultimately empty.
Starting at 9 min in, he talks about his ambivalence regarding Marx, saying that gave him the historical-analytic approach to formulate his questioning of the modern moral climate (including the ethical approaches within Marxism).
Much of the rest will be review for anyone who listened to our two episodes on MacIntyre, but it's nice to hear it from the man himself. In the middle of part 2, we get some more detail on the philosophy of language angle than came through in his book (he cites Peter Geach), all moving toward the relation between being good in a role (a good violinist, a good burglar), and being good as a human being. At 8:45, he responds to the charge that this latter concept is empty by characterizing four sets of goods needed by every individual to flourishing: nutritive needs, family affection, larger social needs, and intellectual virtue. So while there are many kinds of a good life, they will all involve all of these to some degree. "There are standards independent of our feelings, actions, and choices by which we may judge whether this or that is choice-worthy." I suspect that his way of putting this has less to do with his conclusions in After Virtue than in his subsequent proclamation that we can't get rid of biological considerations after all in looking for human excellence.
At the beginning of clip 3, he fills out the argument (again citing Geach) that emotivism doesn't semantically capture our use of moral terms: If you use "X is bad" as equivalent to "boo X!" then it wouldn't mean that in the context of the sentence "If X is bad, then P," which means that what should be a simple logical deduction (i.e. the conditional about IF it was bad, and the assertion that it is bad, to P) becomes invalid.
At 3:30 into part 3, he makes the puzzling statement: "It's only at the level of practice that we can become Aristotelians." This is how he introduces the notion of practice (e.g. "chess player") as we discussed on the episode, and his claim that Aristotelianism isn't just another moral theory (that will in turn be irreconcilable to its opponents in the way that he objects to) but a matter of phrónēsis, i.e. Aristotle's notion of practical wisdom. We can't just sit back in a philosophy class and sketch out objective values to determine verdicts on hypothetical moral dilemmas. Instead, it's only by being in a situation, within a culture with its practice-structures and history, that we can see through practical wisdom what our duties really are. The thrust of his Aristotelian attack starts at 11 minutes into part 3 and continues in part 4. It is our own modern phrónēsis that he thinks leads us to best interpret Aristotle so as to overcome the limitations of his time. To overcome the limitations of our own time, we need to learn a lot of history, sociology, and anthropology, and to engage in a lot of practices and reflection on those practices ("on farms and construction sites, laboratories and studios, soccer teams and string quartets, political struggles and military engagements").
Finally, starting around 5:30 into part 4, he talks about the social pressures within academic philosophy itself: the pressure to publish, and publish on certain topics in a certain way, all to be put into a journal that no one reads. According to MacIntyre, it's about transferring habits of mind: "to shape minds so that they're open to some ideas and not to others." He describes it as a conformist discipline, and consequently that "living on the margins" is necessary to see things as they are. Nonetheless, you need to learn as much as you can from those within the academic center; you need to understand something from the inside and outside in order to legitimately object to it.