Adding features to web video players

Hello everyone

I have a question regarding video players that we see online like the one used on youtube and the other offered by streaming website like vehoo etc.

Most of this video players can be embedded in other website but my question is wether is possible to modify them in order to add more features to the player.

For example one of the easy modification that comes to my mind is the screen size that can be set when it comes to embedding these video player.
However, what if I want to add features like shortcut keys, for example if I press a key while the video is being player then a respective action is triggered or when in full screen I go at the bottom with the mouse a different layout showing the "pause, play" buttons is shown.

What tools are required to make these sort of amendments?