Convert video files in VPS for web site

[pisio]

Hi there.
I create video site. And I got the problem that when users upload a video, I have to convert as much as possible keep the sound quality and video. Some of the videos may have subtitles I want to pull the video file, so I can load them into html5 video player.

I have a VPS that can take the load. I would like advice on how I can convert and separates from the video subtitle, so as to obtain the smallest possible amount, not loses quality sound and picture.

Sorry if I'm wrong section, which should put the topic.
I do not have time to learn by "trial - error" how to do it. So please people with experience to tell me.

Edit : // I prefer to be saved in webm