The mechanism of video is simply a “Flip Book”.
The one used for piece by piece of the “Flip Book” are “Images”.
For example, if you have a resolution of 1920 x 1080 (full Hi-vision) “30 frames / sec”, you need 1800 images in 1 minute.
If you make this as a video, it will become a huge file size of 15 GB in 3 minutes.
Therefore, it is common to use resolution of about 640 × 480 (300 thousand pixels) when saving with uncompressed file (extension AVI etc.).
(Nevertheless, it will be about 1 MB in 1 second.)
If you can not reduce the resolution, you will have to reduce the file size by compressing each image using the “compression algorithm” called “codec”.
Currently, “codecs” are common used as H.264, VP9.
The extension of video files with H.264 is compressed by MP4. The extension of video fileswith VP9 is compressed by webm.
By the way, licensing fee will be incurred as H.264 contains patents.
For that reason, there are hardly any things that can be saved as video with MP4 files with free software that has a video recording function.
(There seems to be many uncompressed AVIs.)