OSD:
a class that is used for overlaying arbitrary bitmaps on the video
-> useful for showing a play, pause, seek symbol, volume bar or progress bar

Subtitles:
There is media data with subtitles embedded (and there exist also external
subtitle files). One possibility would be to add subtitle selection to the
VideoPath, another to add it to the MediaProducer and a third to create a new
class that operates on a MediaProducer or VideoPath.