This method works on Windows Media Player.
I haven't tried in others, but it should work similarly.
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There is a subtitle button on the lower right of the Windows Media Player that works on videos.
Push the button or press Ctrl+L on the keyboard and it will have the option to choose a text file (ass/srt).
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Then choose the file(s) for the video
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Then you should be good to go.
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NOTE: You have to do this method everytime you wish for the subtitles to be in the video.