First*, if you haven't already, go here to make sure you have the correct codecs needed to play your video type:
http://medibuntu.org/repository.php
Don't worry, I've been using Medibuntu as a repository for years, these guys are legit.
After that, try installing this:
ubuntu-restricted-extras
If it's already installed, do a complete removal and install it again. This will pick up on a few things, like Flash, but should also specifically pick up on the codecs needed for your video player.
If you need to play some purchased DVDs, you'll want to go through with this as well:
https://help.ubuntu.com/community/Re...ts/PlayingDVDs
*make sure you are legally able to do this in your country, blah blah blah
EDIT: And yea, I don't really use subtitles myself but I'll do a Google and see what I come up with.
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