HitFilm 2017: What's the difference between project video settings and export video settings?
Project settings determine the way your source media will be interpreted (played/processed/pre-rendered) by your NLE application.

Export settings determine the format of the file that you are going to output once the edit is finished.

For example:


  You shoot video on a Panasonic HVX camera in Apple ProRes 422 codec
  (HQ). Then you import the clips into your project. The project codec
  will be Apple ProRes 422 (HQ).
  
  You plan to publish the video on youtube. There is no practical sense
  in keeping the quality as high as Apple ProRes for web delivery, so
  you choose to compress the resulting video into H.264 codec inside an
  MP4 container (listed as Youtube 1080pHD) to make it easier to upload,
  without significantly sacrificing its quality.