EOS 5D Mark IV: ISO Speed with HDR movies

Shooting HDR movies in Full HD on the EOS 5D Mark IV will help you avoid blown highlights in high contrast situations. When selecting the HDR mode, you may find you are unable to select an ISO speed lower than ISO 400. If this is the case and you’d like to set a lower ISO, then you will need to switch out of Tv mode to M or Av mode.
Camera settings
EOS Movies
EOS 5D Mark IV