Tools to merge SRT subtitles

SRTMerger – Input: SRT, Output: SRT, Different colors, displays both subtitles at the bottom, on top of each other.

2srt2ass – Input: SRT, Output: ASS. One subtitle on the top of the screen, one subtitles at the bottom (possible because the output format is ASS).

DualSub – Input: SRT, Output: SRT; displays them at the bottom, next to each other. This is essentially a hack, so it requires you to specify the font with which your player will display the subtitles in advance – you are essentially creating subtitles for a particular player, and it can be a bit fiddly. On the plus side, this one has amazing options for keeping subtitles on the screen for longer, when possible, as well as smoothing over small timestamp differences.

Player functionality

Subtitler (VLC plugin)