With the free Vidcoder can you burn in / hardcode subtitles from external srt files and convert to mp4 or mkv. It might be useful for playing video on devices that doesn't support external/switchable subtitles.
http://vidcoder.codeplex.com/
or
http://www.videohelp.com/software/VidCoder
http://vidcoder.codeplex.com/
or
http://www.videohelp.com/software/VidCoder