I use this website to download subtitles :
http://en.savefrom.net/1-how-to-download-youtube-video/
After you paste in the link and it shows you the video, on the option that lets you select the quality, click it and choose subtitles. And then it'll download subtitles. But however, you also need to video too. And also vlc player since it works best with it. I don't know about a mac since I only have a pc.
LOL this option is great because if you want to edit a video, you'll have all the clips and don't need to crop eng sub out, so you won't need to download 2 sets of copy, one with sub and the other without. And if you want to watch subs, just put it with the downloaded subs.
Tell me if it doesn't work, and I'll help to my best ability.