Why is it if I'm making a video there is no sound

I’ve the same issue. My volume is up and not set to silent. I’ve tested the microphone by recording a memo, and it works. However when using the Camera all to record, I hear a distorted sound and cracking, with my voice reduced to a whisper.

If you are using screen recording then the sound is muted to prevent piracy.

You may want to check this https://support.apple.com/en-us/HT203792 article out to troubleshoot your issue. If it still doesn't work you may need a repair.