[invalidator]

Reducing framerate doesn't help much when there isn't a lot changing between frames. Here are some better optimizations:

Noise reduction, so you compress less useless noise: -vf hqdn3d

Turn up the Constant Rate Factor. This will make better visual tradeoffs than decreasing frame rate. 23 is a good starting point for h264, but keep increasing it until you don't like how the content looks: -crf 23

Throw more CPU at the problem: -preset veryslow