The Preload button present in the import footage panel is used to choose whether the video footage on which you wish to work is to be read directly from the computer storage support or if it is to be included in your current project.
This option is important for the following reasons:

* Let's assume your projects possess layers composed of non-preloaded video footage.
When loading the same project again, TVPaint Animation will look for the data necessary to display the images, layers and timelines in the external video files. This function is interesting as it saves space when saving as your project does not contain all the images it comprises.

Attention however: if the video file to which your project refers is deleted, modified or renamed, this will have an incidence the next time your project is loaded (the layers and images concerned will not be found…).

* To avoid having a project which is dependent on external videos, you may, when video footage is imported for the first time, preload it immediately. Your project will then be more voluminous when saved, but at least there will be no risk of loosing the data when the imported files are modified.

If you forget to do this, it is possible to preload the files later via the main menu Project > Dependencies > Load all. This menu also displays the path and name of files on which your project depends.

* In addition of images and videos, sound tracks can be linked to your project. To know more about, please read lesson 8