Usually it is the file name or the encoding, not the conversion. The .srt has to sit in the same folder as the video and carry the same base name (movie.mp4 and movie.srt), otherwise the player will not pick it up on its own. If the subtitles do appear but accented or Cyrillic letters look broken, the player is reading the file as ANSI. Switch its subtitle encoding to UTF-8 and they will be fine. Some hardware players are also picky about a language suffix, like movie.en.srt. To rule out the file itself, open the result in our
online SRT viewer and check that the cues are there with sane timings.