clip with screen overlay mode makes underlying fades not work

[Michiel]

btw. it seems to only happen with the “screen” and not with the other keying effects.

[Steven L. gotz]

Try using nested sequences. Place the screen clip above the nested sequence.

[Tim Kurkoski]

I was able to duplicate the behavior, and did some experimentation to find the answer. This has to do with how Premiere Pro’s rendering order works. This is from the help file (under “Adjusting Opacity”):

Rendering order affects how opacity interacts with visual effects. The Video Effects list is rendered first, then geometric effects such as Motion are rendered, and then alpha channel adjustments are applied. Within each effects group, effects are rendered from the top down in the list. Because Opacity is in the Fixed Effects list, it renders after the Video Effects list. If you want opacity to render earlier or later than certain effects, or if you want to control additional opacity options, apply the Alpha Adjust video effect (see Applying and controlling Standard effects).

In effect, what this means is that the Screen key effect is processed before the opacity keyframes are. The end result is that the frames for the top clip (the one with Screen applied) are processed before the lower clips are processed, so the full strength opacity of the lower clips are used in the Screen key calculations.

I tried using the Alpha Adjust effect as suggested, but it didn’t help. That’s because the opacity adjusted clips are lower in the timeline, the Screen effect is still calculated first.

There are a couple of workarounds I found, though:
* Pre-render your opacity adjusted clips out to an AVI file, then replace the original clips with the AVI.
OR
* Place a black video matte below the opacity adjusted clips. You may need to add a video track and push everything else up a track.

I’m not quite sure why the second one works, as that goes against the logic of what the help file says. My only conclusion is possibly that when the Screen effect is being calculated, it looks at the accumulated opacity of the rest of the sequence, but doesn’t take the default “black background” into effect. Adding the black matte forces the effect to calculate the opacity of other clips on top of it. Just a guess.

(To answer some folks’ question: Yes, I tried nesting the opacity adjusted effects in a second sequence, but that doens’t help. Premiere Pro’s rendering order behaves like AE when the “collapse transformations” switch is turned on for a nested comp; it doesn’t render one sequence before the other.)