Help for subbing

Hi everyone,
I'm part of a forum where we sub things, specially Japanese PV. I've recently moved to mac and since then I had so many problems with my work. I just want to do two main things.

• The first one is to cut various formats of video, as mkv or mp4 to take the song's video I want to subbtitle.
• The second one is to burn these subtitles in a high quality.

I've tried so many softwares but there was always loses of quality so that when I uploaded the video on Youtbe, for exemple, the quality was awful...

So do you have any magic software that could, finally, help me to do my job ?

Thank by advance, and sorry for my poor English :D !