If you find that your subtitles are not showing even though you've installed QuickTime 7, the most likely culprit is that your movies are being opened with the QuickTime X Player.
The easiest solution to this problem is to set the QuickTime 7 Player as the default movie player. Here's how on the Macintosh:
1. In the Finder, select your subtitled movie file, e.g. "export.mov"
2. Select File->Get Info from the menu. (Or type Command-i)
3. Look for the item named "Open with:". If the disclosure triangle is closed, click it to open it.
4. The popup menu probably shows "QuickTime Player". Click on the popup menu and select "QuickTime Player 7".
5. Click on the "Change All..." button to make QuickTime Player 7 the default player for all movies of this type.
Now you should be able to double click on any .mov file and have it open in QuickTime Player 7 by default. If you need to revert back to the QuickTime 10 player by default, just use the same steps, selecting "QuickTime Player" in step 4.
For more information on why you might need to install QuickTime 7, see this support article.