So it's worth knowing that straight alphas are best for Qlab but if you open clips encoded this way in quicktime player you might no see the true result. With the straight the text is visible at 100 percent through to the end of the fade With the premultiplied version you see the fade correctly Your example of white text with a fade even plays differently in QuickTime Player and in the finder quick view. There is a huge variation in how video editing and compositing programs handle alphas. The solution is to use a straight alpha not premultipled (presumably with black) Does it seems like something you can solve? I have put in attachment the video from Final Cut Pro 7. So it seems that QLab and Final Cut Pro 7 shares the same (bad) way to handle alpha. I have tried to superpose those 2 clips in Premiere and there everythings works fine BUT in Final Cut Pro 7, it is exactly the same issue as in QLab. Instead it changes color to black in 14 frames then stays black for some frames and then fades out for the rest. There seems to be a kind of problem with the way Qlab handles the alpha channel.The title should fade out at the end for 28 frames. One is a background in full screen and the second one is a title in ProRes 4444 with alpha. And in any case, a switch or checkbox would take all the guesswork out of things. I seem to remember a time in the recent past that alpha was interpreted as straight in QLab, so premultiplied would show up with a black halo, or a darkening in semitransparent areas, so it is conceivable that things could shift again. This would also help in case things in AVFoundation or in MacOS or on different hardware change unpredictably over the years, so that bringing an older QLab show back online can always be done. Also some other media servers out there work better with straight alpha, and it may be the case that a show gets ported between media servers, so having a way to use either straight or premultiplied would be great. This is an unfortunate QLab-specific limitation for workflows that center on that encoder. One challenge is that as far as I can tell, Adobe Media Encoder does not currently have a way to specify alpha way After Effects does, and I think what it generates is straight alpha, which means it is currently not usable as an encoding tool for QLab. I am currently finding that rendering premultiplied from After Effects is working in QLab, as you demonstrate here. It is true that I had a similar conversation with TroikaTronix regarding Isadora a few years back, and the result was the addition of that user-selectable switch to identify the alpha mode, which is very helpful and if it were not too difficult to add to QLab, it would be really great. Thanks for this very thorough look at things.
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