Summary of how to fill the background of Vertical videos in DaVinci Resolve:
- Open Effects and navigate to Open Fx > Filters > Resolve FX the search for Blanking Fill
- Drag this effect on to your clip
- In the Inspector under Effects, fine-tune the effect. I like these settings:
- Fill Extent > Zoom Mode > Zoom to Timeline
- Fade amount: .5
- Fade color: Black
To apply the same effect on multiple clips:
- Right click an existing clip with the effect applied and choose Copy
- Select the clips you wish to apply the effect to, right click them and choose "Paste Attributes"
- In the window that pops up make sure Plugins and Fusion Effects is checked off then click Apply.