See my post 845 here. I used a pen that has an audio & video recorder in it. It also has a dim yellow activity light on the back which I put a piece of electrical tape over.
The pen has a 4G memory. I believe I got a good audio of the DVD, but it kept turning itself off during the Service Talk after the WT. I had failed to recharge it the previous night and it was turning itself off due to lack of battery power. It was really the first time I had used it. To tell you the truth, I haven't really listened to the audio recording to see if it is good. The DVD was rather unremarkable, beyond some interesting footage of Africa, S. America, and N America, and their respective peoples.
Their was an interesting take on Acts 2:11, the phrase "speaking in our tongues" seems to be the basis of the presentation, with the emphasis on presenting the good news in the mother tongue of the hearer.
The "secret" presentation was . . . what can I say . . . I think it was 'not-to-be-recorded' in order to maintain expectation for other congregations who had yet to see it. That's my impression anyway. There was nothing 'secret' to the presentation itself.
If their is any 'secret' to their translating, it is that they are translating the Bible from the English NWT only. Those shown translating were only consulting dictionaries in their own language, not Hebrew and Greek. So they are probably under instructions not to question the accuarcy of the English translation. (Narkissos and Leolaia have many good posts on this subject. One day I might make it a 'study project' just to peruse their posts.)