ok, let say it easy, when you have zero knowledge about video encoding, than first inform how to do it.
video encoding is extra and the vita forum is not made for it. its a lot of information what you need.
MP4 = container, not the codec.
Bitrate for 720p on MP4 = mostly 2000k to 5000k
Audio Codec extra and go into the MP4 container.
srt files subtitles
to many information, you need seperate encoding forum.
otherwise try first and ask later and not before, I dont get it.