To record you will first need to enable webcam access (for Flash plugin and recording application).
Then you can start recording in sync with video, either from video start button or recorded start button.

Approve webcam and microphone access from plugin container and browser: when webcam is available for recording a PLAY button will show below. Make sure you show in webcam preview as expected. If necessary, select a different camera, change your position or lighting. When you are ready click on PLAY button above!