Qlab Alpha fading problem

Alex

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Jun 12, 2021, 8:32:13 AM6/12/21

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Hi all I'm building a show I have a background video loop nothing fancy on there,

and I'm adding an alpha channel clip on top. the issue I have is on the alpha clip there are two images that fade on but they almost flash as they fade on if that makes sense which I don't want.

I have put them together in final cut and they are fine but that's not how I want them I have multiple going on and off, seems to be an issue with qlab?

the alpha clip is Prores 4444 alpha+RGB color is straight (unmatted) built in after effects

thanks,

Alex

micpool

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Jun 12, 2021, 12:04:42 PM6/12/21

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Try re rendering premultiplied, but make sure the background color of the AE composition is black.

Mic

Alex

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Jun 12, 2021, 12:21:33 PM6/12/21

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Mic Legend! Thank you so much, that has sorted it

Thanks,

Alex

micpool

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Jun 12, 2021, 12:56:26 PM6/12/21

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Great! I have to say though I’ve never worked out why sometimes QLab has problems with some RGB+alpha files. Sometimes straight has problems, sometimes premultiplied. Although often premultiplied problems are because the background color is not black, I have had instances of straight and premultiplied files not working. Generally re rendering in the other flavour solves the problem. One day I’ll get round to investigating this properly. It seems there is something that Adobe progs and final cut can read so they always interpret these files correctly, that QLab sometimes misses, but that is probably an oversimplification.

In general my rule of thumb is,

First try rendering with premultiplied with black (black composition background)

If that has problems re render with straight alpha.

I don’t think I’ve ever had an AE composition , that hasn’t been able to be rendered with alpha to play correctly in QLab using one of these methods.

Mic

David Bengali

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Aug 11, 2021, 3:28:32 PM8/11/21

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fwiw, the solution that Isadora has given to this issue is to add a setting on the movie player that lets the user say whether a particular video file has straight or premultiplied alpha. this works out quite well and doesn't require the software to guess.

Tommy

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Sep 27, 2022, 4:16:10 AM9/27/22

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Hi there.

I faced a similar issue in QLab 5.0.4.

The same flashes occurred whether rendered in HAP or ProRes. Ae2022 composition background color is black.
For the time being, I got rid of the problem by playing JPEG or HAP black source at the bottom layer of each group in QLab.