Superimposition changed from 16 to 17?

Hello,

I opened a HD Resolve 16 project on Resolve 17. Everything's fine except that 4:3 clips, placed on V2 as B-Roll, are superimposed over the V1 16:9 footage without vertical black bars (which is what I see on the export rendered by Resolve 16). Rather, the bars reveal the underlying V1 footage. I can't remember if this was a setting somewhere on Resolve 16 but it seems something has changed in 17. How can I quickly change the way a V2 clip is composed over V1 (without going to Fusion)? I don't see anything in "Composite Mode" that might help.

Thank you.

It was a bug in 16 that got fixed in 17.

Clips that don't fill the frame will now correctly show whatever is underneath around the edges.

If that's not what you want, you'll have to add a Black in there.

Thanks. What's the quickest way to do this? Is there a tick box somewhere (such as "treat alpha as black")? Or do I need to put an empty black frame on V2 and put the clip itself on V3 (which would be very annoying to do each time just for B-Roll)?

Black clip on V2 method.