Size is not only dependent on the length of runtime.
See, I compressed this 35+hrs course down to 3.5gb, the price you pay is:
- lower resolution (720p instead of 1080p),
- lower audio quality (56kbps mono used, original was probably 256k stereo),
- more capable video compressor codec (h265 instead of h264)
- video compression is also set to lower quality settings to allow for higher compression rate
- and finally video frames per seconds shown went down to 5 from 30.
All of this is to be able to store less data.
Every setting is there to store less information about the video and audio while trying to keep a quality that is still usable (or should I say enjoyable?).
[ There are courses that are uploaded in 4k which is really a humongous waste of storage space. Designcode courses are sometimes recorded in 4k, older computers (without a capable hw decoder or cpu) can't even play those without stuttering, or the cpu pegged at 100%. ]