Incorrect fps of 2 Autofocus Arducam IMX519 CSI cameras on Jetson Nano

I have been recording videos with 2 IMX519 cameras on a single jetson nano at 120 fps in 1270*720px, however, when analyzing the videos, the frame rate seems to be reduced for both. I saved the videos in mkv format. The documentation says that it can record at 120fps, so is there any way I should encode the video to ensure the fps is preserved?

Please try the command below to see if the framerate can be close to 120fps.

v4l2-ctl --set-fmt-video=width=1270,height=7200,pixelformat='RG10' --stream-mmap --stream-count=-1

That command needs to take into account that I am running 2 cameras simultaneously, and the output just works for a single camera. I want to know if the fps are preserved when you run 2 cameras simultaneously vs. just one.

Also, I would like to know what are the parameters that influence the output frame rate. Even though I am recording at 120fps, the output .mkv file is always less than 120, it varies between 90 and 110. How can I preserve all the frames as defined in the pipeline, or how can I optimize it ?