I think, personally, that aikido videos should be used as a visual reference mainly. I've only watched two, and they were both essentially silent (well, there was drumming) and they were pretty helpful. I think if narration gets further than general (and helpful) statements like "keep moving!" that it might not be the greatest thing.
The one video I have is a collection of Kihon Gi techniques preformed by a French sensei called Jaff Raji. It's about 90 minutes long and deals with attacks "sur la base de shomenuchi" (or something like that). i.e. all the attacks have the same vertical from the front kind of vibe. And it's a wonderful reference for when I've forgotten a technique.