@cahrens @peter-fogg  In HTML5 player youtube you need only one video link and one subtitles link.
In HTML5 player non-youtube you will need 3 fields for different sources of video for cross-browser compatibility.
All speeds for video and subtitles will be adjusted automatically in player itself.

My question was related to videoalpha supporting not-html5 youtube. In that case  we use same speeds that video player does, it was misunderstanding. Don't mind about this.