This is in fact exactly the approach that my lab has been working on for the last several years in developing a media player for language-learning applications

This is in fact exactly the approach that my lab has been working on for the last several years in developing a media player for language-learning applications (which has actually also been used for teaching linguistics and introductory chemistry, so clearly the pedagogical benefits generalize beyond just language learning). Being able to switch between text-centric and video-centric views freely has been a goal of my (now-former, because he just retired) boss for a while (and by "a while" I mean he did his dissertation on interactive, text-augmented video technology with applications to education in the 70s), and we're not quite there yet, but we do have the ability to show a transcript that can be synchronized with the playing video (automatically scrolling and with highlighted text to show where the video is), or scrolled freely and searched through to select a specific part of the video to skip to. You can see an implementation of the technology (including playing around with some of our editing tools) at http://ayamel.byu.edu http://ayamel.byu.edu