A Media Data (mdat) box contains the media data payload for the F4V file. All video samples, audio samples, data samples, and hint tracks and samples are contained in the mdat box. See 1.8 Supported Media Types. The mdat box occurs at the top level of an F4V file, along with the Media (moov) box. The mdat box cannot be understood on its own, which is why a moov box must be present in the file as well.
