VLC is does not support hardware video decode on the Pi by default. There are instructions to build it yourself with hardware support (somewhere on these forums), or you can use OMX Player, which is included in Raspbian and does support hardware decode.
OMX Player is a command line application, but you can configure it to launch from the file manager when you double click on a video. There is also something called OMX Player GUI, which might be your simplest option.
To get the file manager to correctly launch OMX Player with a double-click on the file.
- Right-click on the file you want to play, go to open with, and select custom command.
- Under Command line to execute: enter, omxplayer %f -b
- Check, Execute in terminal emulator
- Add an application name, and check Set selected application as default action for this file type.

You will have to do this once for each file type (mkv, mp4).
After that, double-clicking on any file of the same type will launch it in OMXplayer. Hot keys work when configured this way. Hit "q" to quit playback early (omxplayer --help, or man omxplayer for more info).
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?