Convert SRT to SUP

You can certainly create 3D subtitles for 3D movies in several special utilities made for this particular purpose. You can take any of the common subtitles, such as .srt files and turn in to a 3D variant, for example in .sup files. Such srt to sup conversion is done because using standard subtitle files for 3D movies would provide sub-par viewing experience and the 2D subtitles would feel odd while watching in 3D.