media-video/
subtitler-yuv

for mjpegtools for adding subtitles, pictures & effects embedded in the picture

http://panteltje.com/panteltje/subtitles/

There are no pull requests

You think something is missing here?
Start with filling a new pull requests.

If you also like to help the Gentoo project, you can consider sending a Pull Request via GitHub.
Before doing so, you might want to take a look at the wiki page.