Firstly, mp4 videos aren't compatible with Ren'Py
You'd be doing yourself a favor by reading
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at least twice.
The "best" way is too broad, the "easiest" way...
put this somewhere:
Python:
init:
image myvideo = Movie(size=(400,560), channel="mychannel", play="video/sexy video.webm", loop=True)
when you want to show the video:
Python:
label start:
show myvideo
when showing the video it can take positional arguments:
Python:
label start:
show myvideo at truecenter
The "best" way depends on what your doing. It could be just a pop up video, an interactive scene, part of a screen, or God knows what else.
My advice, if you don't have a preference just use webm (common and compatible) videos and keep them as close to 24 FPS as possible.