How to Upload Handheld Gameplay Footage as a Thumb Player in Rhythm Games?

Unlike index/multi-finger players who fix their devices on a surface, thumb players hold their devices (handheld), which causes the screen to shake severely, change position, and potentially lead to "the gameplay isn't visible" rejections. So, it's better to reduce device shake and camera drift, right? For my Arcaea gameplay footage, the recording device is fixed (though I placed it on a bunk bed ladder). To stabilize the playing device's position, I played with both elbows tucked firmly against my body, keeping my back straight, and carefully maintaining a horizontal position so the device was clearly visible for recording. Is it uncomfortable? Yes, it is. Asking someone who plays holding the device vertically to suddenly play horizontally... But this was the best I could do.