Hello, I believe this behavior should be classified as a bug unless it’s by design which needs to be confirmed, of course.
How to reproduce:
- Create 2 video tracks. The bug is not about the number of tracks but the second track makes it easily visible.
- Add one clip on the top video track and any not blank image on the bottom track.
- Cut the top track into 3 clips and apply the opacity filter of 50% to the middle clip.
- Produce cross fade dissolve transitions between middle and left and right and middle clips.
- Move the image on the bottom track underneath the middle clip with the opacity effect and resize it so its duration is the same as the middle track plus both transitions.
- Play the video starting anywhere before the left (first) transition.
Observed behavior reproduced consistently:
The video will not smoothly transition on the left side of the middle clip but will smoothly transition on the right side of the middle clip.
Expected behavior: smooth transition on both sides of the middle clip with reversed effect: smooth fade in of the background image on the left and smooth fade out on the right.
This effect does not happen with other filters, for example, the blur filter and/or text filter will work smoothly (fade-in on the left and fade-out on the right).
I haven’t tried with all existing filters, but the opacity filter definitely has a problem. I guess something in the transition algorithm incorrectly calculates the pixels when the opacity on the right side of the transition is less than 100%.
Is this urgent? I guess not, because it can be worked around by creating two tracks with the same content and applying fade-in/fade-out filters manually, which is doable but really time-wasteful and error-prone.
So, because some other filters work (which is really nice especially when adding a text filter) I suppose the approach is correct but something was not tested with the opacity filter. Just wanted to let you know.