GOS-user
The file size of a video depends for example on your settings (e.g. resolution, frames/sec, bit rate, HDR, video format (e.g. H.264 or H.265/HEVC)) as well as - although less relevant than the former - environmental conditions: For example, fast-moving objects in the image or detailed subjects may require more storage as they are more difficult to compress.

It can also make a difference which app you use, even with the same device. File size -filming the same subject with the same settings (resolution, frame rate) - differs depending on whether you use the GrapheneOS camera or the Pixel Camera app, for example.

I have just carried out a - non-representative - test (just so that you have a comparison value): A one-minute 4K video (3840x2160, 60 fps, H.264) is 527MB in my case.

Maybe you find this site helpful - it doesn't go into too much technical detail, but shows, for example, estimated 4K video file size per minute recorded by iPhone, Samsung etc.

https://www.winxdvd.com/resource/4k-video-file-size-compress.htm

How can I compress a video or, even better, change the resolution settings? I looked in settibgs and couldn't find any options...

    GOS-user

    I can give you some tips for GrapheneOS and Pixel Camera:

    GrapheneOS camera
    Triangle top left > Video quality> choose between UHD, FHD, HD and SD.

    For photo (not video) you can also reduce the quality in the same menu under more settings> Image Quality.

    Frame rate and file format currently (version 66) cannot be set.

    Pixel Camera
    Open app, tap on video icon then on the gear wheel at the bottom left. Adjust the options "Resolution", "Frames/sec", 10-bit HDR.

    Video format can be changed under more settings> advanced> store videos efficiently.

    I have not tested this, but "Social media depth features", "Rich color in photos" and "Ulta HDR" could also have an influence on the file size - you would have to test this yourself.

    Note: Depending on the device model, not all settings may be available to you.