Some video editors or converters can help you like Corel Video Studio or Tenorshare Video Converter. You can add subtitles by Corel Video Studio directly. Converters can help u add when conversion.

Some video converters can do this. I just know Tenorshare Video Converter, it has both MAC and Windows versions. This program is well reviewed. I am not sure if it can help u.
Hope this can help you