Background & transparency
Every generation is rendered either on a solid background or with a transparent one. The transparent option gives you an alpha channel, so the animation drops onto whatever is already on your timeline. You choose this with the background chip in the composer, before you generate.
The two options
- With background: the motion sits on a solid fill. The output is an MP4 (H.264) with the background baked in. Best when the clip stands on its own.
- Transparent: the motion has an alpha channel and no background. The output is a MOV (ProRes 4444) that carries transparency, so it layers over anything beneath it in Premiere. Best for overlays: lower thirds, callouts, logos, anything you want to sit on top of your footage.
The background chip reads BG when it's solid and No BG when it's transparent. When you pick transparent, the summary line under the composer adds · Alpha.
When to choose which
Choose Transparent when the animation goes on top of other footage: a title over a talking head, a logo bug in the corner, an animated callout pointing at something in the shot. The alpha channel means no box of background hiding your video.
Choose With background when the clip is the whole shot (an intro, a full-frame data animation, a standalone card) and there's nothing underneath it that needs to show through.
Transparency is normally decided at generation time: the background chip picks the output format. There is one way to change your mind afterwards without paying for a new generation. Open the customization controls on the result screen. If the clip has a background, the controls include a Show background toggle. Switch it off and render again, and the clip comes out as a transparent MOV. If a generation doesn't expose that toggle, generating again with the Transparent option is the only route.
A transparent MOV is heavier than an MP4 because ProRes 4444 stores 10-bit color plus the alpha channel. That's expected, and it's the format that lets Premiere composite the clip cleanly over your footage.