There's a service in Japan where you can associate text to a point in a video. You type text like chat while watching a video, and the text is recorded with the timestamp and played back along the video. Association is bidirectional---you can jump to certain time point in the video from the text as well. Currently most people just making fun, putting funny text on videos, but it would be quite useful to attach transcription by collaboration of audiences.

Unfortunately they only provide closed service for registered users: http://www.nicovideo.jp/ (Actually they originally used YouTube as a video source and had no access restriction. But they got so much popular that YouTube had to shut down access from their site.)