Many people start a song, hit record, and find the music has paused or dropped in volume. This is because recording uses the microphone, and iOS manages audio between apps.
Things to try
- Start your music first, then open your camera app and record.
- Check that no other app is holding the microphone, such as a call or voice recorder.
- Use wired or Bluetooth headphones for playback so the microphone does not pick up speaker sound.
- Try a camera app that is designed to leave other audio playing.
Results depend on your iPhone, iOS version and the app, so test a short clip first.