It works for any video format (YT, .avi, .mp4, .mpg, etc.)
1 gig = 3 min video maximum (see my extras for more)
You will get a .srt file containing the subs. You just have to name the sub file with the same name than your video file and place them together in the same folder, and the subs will automatically be added to your video when you read it.
The format I use is Youtube compliant, you can add the .srt file to your Youtube video to enable the subtitles !
I can also translate the subtitles (only French > English, or English > French), see my extras below.