Currently, it is possible to add images and video files to each layer in Producer from desktop, web or assets from your campaigns.
Option 1:
How to add an image and videos from desktop or web
1. Press the '+' button on the layer you wish to add your new asset to
2. In the window on the right-hand-side select 'Media file'
3. Input a source title
4. Upload the file
Option 2:
How to add assets from the campaigns:
1. Press the '+' button on the layer you wish to add your asset to
2. In the window on the right-hand-side select ''Video asset"
3. Select a campaign
4. Select a video
5. Drag and drop it into your layer