I use Dropbox and VLC to watch movies with subtitles on my Iphone. Definitely need subtitles, too many mumbling actors and actresses these days. Amazon was genius to put subtitles on its movies, At least the ones I have seen. I suppose Netflix does the same but have never used it for streaming movies. Aside from Amazon streaming....I also use VLC and add subtitles (easy to do w VLC) snagged from subtitle sites.
Subtitles are the greatest thing since sliced bread! As long as you name the subtitle the same as the video file most movie players will automagically load them. (VLC will,Imovies won't.)
I don't do streaming but have a movie library of 1500+ movies and 86 TV series from around the world,all with subtitles.(I've come to view old silent movies as an art form.)
GET YOUR HEARING CHECKED!
I thought they mumbled too before I got hearing aids.