They would need to be separately and independently represented. But on news and documentary programmes, it is mainly the other way round with the meaning carried by a carefully scripted sound track and images used to illustrate or merely decorate the words. There is a single logical structure of scenes, but no simple mapping to time and media. This point is connected to the work by Lynda Hardman and others on multimedia authoring languages. Note that the display hierarchy of pages, lines, words and characters does not have a simple mapping on to the structural hierarchy of sections etc.
Automatic extraction has little part.
Readers cope with a wide variety of these. It uses automatic extraction i.e. it automatically re-processes documents to use all the words in them and nothing else to build new indices that are used by its software. Its main use is to search collections that are so big they couldn't possibly be searched by hand nor marked up again for this new purpose. The main lesson is that multiple alternative indices will be required. They could all use, underneath, a common scheme for referring to places in the video in terms of minutes, seconds, and frames.