Generally speaking, you cannot convert any image file type directly to APK. However, some apps can use images or even videos to create rich and sometimes animated wallpapers for Androids, which means mp4 to apk conversion may be possible. These are generated as APKs, i.e. programs that are installed and run in the device to replace the wallpaper.
So it is really not a conversion per se, more of generating a simple Android app that contains the image your video you import in to.