Part of the problem is that if the subtitle track isn't hard coded, the tv has no way to go select subtitles (VLC does this easily, but Samsung, not so much). I can only access them via VLC on the desktop. I have been able to convert the mp4 to .avi with the result that the subtitles are no longer accessible anywhere -- not on the desktop and if that won't work, the tv sure won't be able to get them. The only other alternative is to become fluent in Spanish, and while i might pull that off in another year or two, my husband won't, as he's not learned the language.
I've done an info grab on the file and it says this:
MPEG-4 movie
Codecs: Subtitle, AAC, H.264
Like I said, if it had .srt files, I could work with a video editor to hard code them, but it seems to have multiple language options, and no separate files for the subtitles.