The recorded video shows only a black screen

(I'm a non-English speaker, so I use a translation app.)

I had a meeting for about 4 hours. Then the size of the recorded file was so large (about 20GB). Also, when viewed with VLC on a mac, a black screen appears for 40 minutes, and for 4 hours when opened with Quick Time Player.
The video file is large, so I'm wondering if I can somehow restore it.
Does anyone have similar symptoms?