Transparent image suddenly switches to all black, blocking video underneath

[mperkins]

I’m new to Shotcut, but think I’ve found a bug with transparencies.

I’m using the program to edit together some footage from a bike ride, which I want to annotate with titles. I stitched together the video in one track; to allow for the titles to be easily editable / changeable, I created a transparent PNG image and imported that as an image into a track above the video track, and added titles to the image, along with a fade in and fade out (using “adjust opacity instead of fade with black”). I copied and pasted that image in the “text” track to get additional title screens.

This worked beautifully: I was able to see my titles fading in and out as text overlaying the video as the clips played underneath. It was exactly what I wanted! However, once I went to export (using the default settings), everything changed: all of a sudden whenever the text was supposed to show all I got was a completely black screen with the text as white on top of it. I’ve played with the “blend mode” for the tracks (over, none, add, …) and it doesn’t seem to change anything at all.

This looks a lot like the issue posted about here, which I don’t see a resolution to. I’m using Windows 10 with Shotcut version 19.04.30.

Is there anything I can do to fix the broken transparencies?

I’ve attached an image showing Shotcut mis-displaying the transparent image as all black. I’d be happy to share one of it showing the clip underneath and the transparent image, but the forum is only letting me attach one file.

[sauron]

Try un-hiding V2.

[mperkins]

That did it! Once I unblocked all the video layers underneath (had V1 as well), it started showing the transparency as transparent again. Thank you!!!

As a side note, I’d had those layers un-visible for quite a while; any idea why it suddenly started not showing the text layer as transparent once I exported the video?

[sauron]

I really don’t know why hiding lower tracks messes with transparency. It only seems to happen when the track has a clip(s) on it and the transparency goes black when the playhead is crossing the clips. Transparency works fine in the gap between clips. It probably has to do with how compositing works.

@mperkins

I created a transparent PNG

You don’t need to create a transparent png. You can use Open other > text to create text clips.

Or you can open a transparent clip and apply text to it.

Click OK and you’ll have a transparent clip in the viewer.

[mperkins]

Thank you very much!

[shotcut]

@mperkins

had V1 as well

This is the critical one. All upper tracks blend with V1 instead of some hidden transparent black track. This is for performance. Otherwise, with just video on V1, it will continuously be trying to blend, which has a cost - more so if there is any non-opaque video on V1. If you really want everything to blend with a transparent black (or other color) track, then make it yourself by placing only a transparent Color clip on V1 and stretching it to the full duration as needed.