IOS11 - Problem with recording screen with sound

So today I was looking around at the features of ios11. I came across the record screen button, so I decided to record my screen while I was watching a video from safari. I then went to view my video and didn't hear anything from the video I recorded. The video was playing fine but there was obsolutely no sound. I tried everything. I also tried unmuting and muting my mic which didn't help.