Starting with iOS 11, you can record your screen (and audio):
Awesome feature, however when I tried to upload a video I recorded to YouTube the audio did not work.
Turns out iOS 11 records two audio tracks, the 1st one being silent 😡
You can remove the silent audio track with
ffmpeg very quickly
ffmpeg -i input.mp4 -map 0:0 -map 0:2 -c:v copy -c:a copy output.mp4
If you are on macOS you can install ffmpeg by running
brew install ffmpeg