Currently Being Moderated13-Sep-2011 05:04 (in response to leopoldofrommexico df)
It is possible to use .SRT files with movies in QuickTime Player by installing Perian. However this does not work on the AppleTV 2.
I suggest you look at these two program. The first is Submerge, this 'burns in' the subtitles so they are part of the video, with this approach the subtitles are always on and cannot be turned off since they are now part of the video itself. The second program is iSubtitle, this adds the subtitles as a proper QuickTime subtitle track which can be turned on or off, you can even include multiple languages. As the subtitles are converted to a proper QuickTime subtitle track they will work on an AppleTV 2 unlike a separate .SRT file.
Both programs are actually produced by the same company. See http://www.bitfield.se/index.html