Testing your application, I noticed that various YouTube URLS have, and can play in the browser, higher resolution MP4s than Elmedia Media Player PRO can play (let alone download).
That is, a video link may afford (through YouTube settings button) 1080p, but EMP PRO only shows 720p and lower resolution instances in its drop-down UI control. Or, for another YouTube URL, 720p may be the highest resolution MP4 to view, but EMP PRO only shows 360p and lower.
So, according to the results I observe, EMP PRO does not support playing (or downloading) the highest resolution(s) of YouTube video.
 Ok, I see that the highest resolution MP4 can be accessed in EMP PRO's Browser Window. My complaint still applies for the Player window, however.