Static frame video and a motion-intensive appendix: how to render fast?
As I can see, you know duration of your song, it good.

I can suggest this trick:


Generate 5 second of video with static image. With good settings, good fps, slow encoding and so on. Video must be without audio.
Join this video with itself as many times, as you want, so duration will be a little more of your clip. This operation not requires reencoding, so can be performed very fast.
Split your clip to exact size as you need. (no re-encoding)
Join outro to file
Join your file with audio (without re-encoding for video, but audio you can modify based on your needs. If you want to upload it to youtube, you can not reencode audio, youtube does it itself)


This can be pretty fast.