Pixelated stream for few fps games ?

[Punjara]

For some games (FPS), while I stream on YouTube, I get very pixelated streams. I use bitrate above 20k with x264 encoder, CRF 17, Key Interval 2, Cpu usage preset : superfast, profile : High. These games include Far Cry games (Dunia Engine), Horizon Zero Dawn PC (Decima Engine) and may be more, just experienced pixelation in these two games.

Horizon Zero Dawn : https://youtu.be/K7vDjg-mY78
FarCry 4 : https://youtu.be/kUf7AGia_IA