Watch videos with SUB/IDX subtitles I have video files with their SUB/IDX subtitles.
I'm using MX Player Pro but it does not support SUB/IDX subtitle.

SUB/IDX subtitles won't display.
SUB/IDX subtitle is not supported as of yet. It will be supported in the future.

How can I watch videos on my Android device with SUB/IDX subtitles?
You can use VLC to view videos with subtitles. Copy the subtitle files on the same folder as the video, then change their names to be the same as the video (don't change their extension).