F-Stop has always written tags into files only for JPG files. For all others F-Stop writes it into sidecar files. However we plan to add more files to the list of formats for which we will embed tags. However, videos are not planned, since sometimes you can not just change couple of bytes of video, but need to rewrite whole video (which can be several GB in size). Also, due to how Android works with SD cards, sometimes we would need to even copy it twice.
goran
