Fixes #54 also added `libx265` video codec

[buddhhu]

It fixes #54 and added option to change video codec between libx264 and libx265

libx265 will convert the video into HEVC format which uses less size with negligible change in quality.

[gbdomubpkm]

Could this be merged ? There are so many videos that I can't compress, and i don't know why. I would like to test if this improves things. Thanks.

[caydey]

Appreciate the pull request, I've used it as reference to implement the changes myself as many changes were required