It's already an mp4 I bought from iTunes, high quality. The video is a minute and nineteen seconds long, and goes from 8 megabytes before and 32 megabytes after, both being the exported results as mp4's. As you may or may not know, the author controls the time length of the composition, so the song cuts off automatically. I have also shortened the song on the timeline for good measure and hasn't made a difference. I've also tried reducing the quality of the audio and video through the render options when I queue it, but trying to render the video this way causes the program to freeze for about five minutes before responding with a cryptic message and about restarting the program. Even the song file size is only 8 megabytes, so the finished production shouldn't be so much. Any helpful advice?
Sounds like you have a lot to learn about video codecs and compression. I would start here: (The third section is about rendering) How to add effects and motion graphics in After Effects | Adobe After Effects CC tutorials