[FFmpeg-user] How to add own, subtitles (resp. pure text) into existing MP4 video?

[Ben]

Assume I have an existing well-encoded MP4 video WITHOUT subtitles.

Now I want to add the text "foobar testtext" with fontsize=18 and fontfamily Verdana into video beginning at 1min23sec and ending at 3min44sec centralized 30 pixels above lower border.

How can I most easily achieve this with ffmpeg?

I possible/necessary the text could be put fix encoded into video and not only as traditional subtitle.