From the best I can tell, videos are completely inaccessible to export filters. This is most unfortunate, since one can therefore not write an export filter to convert video format, or do anything else with video.
Please correct me if I'm wrong, otherwise please fill this hole in Lightroom.
To be clear: when Lightroom renders a photo, it passes it to the next entity in the export chain, be it export filter or export service. The same is not true of videos, which bypass the export filters. It would be better to be able to write post-processing actions that can support video too.