There is no precise technical correlation between pixels and bitrate. For the same streaming provider; higher the pixels, higher the bitrate and vice-versa. Different video hosting providers can offer different pixels even at the same bitrate. Pixels define the resolution of video, while video bitrate is average data size for a video file expressed per second of video. There can be high-resolution videos with low bitrate and low-resolution videos at a very high video bitrate. This imbalance is because of some complicated maths that is used to express what to display on a video with least amount of file size. These maths can force the bitrate for a video at any arbitrary small value while compromising on the quality.You should choose the pixels based on the content of video and target display. Afterwards, choose a bitrate based on limitations of the transmission medium, say internet speed.