Requirements: Lazarus
Download it, open the .lpi and Lazarus and click compile
When started, the viewer opens as a border-less black rectangle.
Right clicking, opens a menu to load the subtitle file (*.srt) and set options.
It will start playing the subtitles automatically.
In the options, you can adjust the speed, change the font or colors, alignment...
On Linux use Alt+Click to move the window around.
Not much tested