Subtractive mask issue (newbie)

Hi. I’m using Shotcut 20.07.11 on Linux, which is generally working well.

Part of the edit I’m working on is a screencapture, with some details I wish to cover, to only show the action in letterbox format.

Consequently I’m attempting to make a simple shape mask on a colour, with the operation set to “subtract”. The colour is the top track on the timeline, but I can find no way of using the black colour I have selected to mask (in subtractive or overwrite mode) the track below. The selected clip in the screenshot below is the colour element I am attempting to use as a mask.

I’ve watched the following tutorial " Mask Simple Shape with Opacity" at
several times but the masking simply does not work for me.

Assistance gratefully received

Try using the Chroma Key: Simple filter instead

You have a filter applied to track V4.
That might be causing the problem.


This is using mask with subtract with opacity on the black color set to 65%.




Thank you for the wonderfully clear instructions, @sauron.

However, after removing the track 4 filters and adding a new black colour with opacity and masking, I still see solid black.

I made a transparent colour to see how filters might work with that, but it is still showing up as solid black, so I seem to have some sort of issue with transparency in general.

I am seeing an error log which may be related:

[Warning] <> file:/// TypeError: Cannot read property 'animateIn' of null

This composite image shows (top) the video below showing fine and (bottom) once the timeline hits the simple colour + mask and opacity that it only shows black. No amount of fiddling on the filter settings help.

Unhide V1

V1 not hidden

V1 hidden

Hi @Hudson55

That worked! I’m obviously missing a key principle here as I had several low-numbered video tracks hidden. Could you point me to any items in the docs where this is explained?

Thanks a ton.

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I’m not sure it’s documented anywhere. V1 has to be on for compositing.
It was a change a few years ago to Shotcut.

It’s been mentioned a few times in the forum on the use of V1.

Thank you very much for that clarification.

Some half-remembered workflow from Final Cut has resulted in a lot of wasted hours!

Anyhow, it is working well now, thanks a lot.

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