Export

Open the Export tab (or press ⌘E). Exports go to ~/Movies/EditAI by default; change it with Change….

SettingOptions
SizeSource (the first camera's size), 4K, 1080p, 720p. Other cameras are fitted into the frame.
FormatH.264 (compatible) or HEVC (smaller)
Frame rateThe nearest standard rate of your fastest camera
SoundThe microphone of the camera chosen as the sound, AAC

The preview and the export are built from the same plan, so what you watched is what you get. Encoding is done by the operating system's own encoders through AVFoundation and VideoToolbox. There is no ffmpeg and no openh264 in the app. Exports never carry a watermark.