recording video using Quicktime but it stops recording the video except the audio

I record videos on my macbook air (fully charged) using an external microphone and my iPhone's camera.

Everything goes smoothly the first minutes but then the screen goes black, and the video only captures the audio from then on. I have already checked the battery settings, turned on 'prevent automatic sleeping blabla' setting, adjusted my mac to NEVER go to sleep. Yet, the screen still goes black after 7-8 minutes and a 10-15 seconds into it, it only captures the audio. I cannot begin to tell you how annoying and exhausting it is.