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I'm using Blender's video editor to overlay an image on top of my video footage. The problem is, I need to mask (make transparent) certain parts of the image that are currently blocking part of the video at certain frames. I am able to create a single frame mask and apply it to an adjustment layer that works as exactly as intended by showing the underlying video. I was able to create an animated mask in the movie editor, but when I apply it to the adjustment layer the mask doesn't work at all. I compared the strip settings of both the single frame and animated masks and they are identical, both using Alpha Over as a blend mode. I followed this video tutorial (times 7:22 - 9:22) but the animated mask is still not masking at all. I'm not sure what I am doing wrong.

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  • $\begingroup$ Here's a video that goes over that youtube.com/watch?v=rXsrkg31VRI $\endgroup$ – stphnl329 Apr 25 '20 at 15:05
  • $\begingroup$ Thanks, but I already watched that video. The guy is using preexisting mask files. He doesn't show how to do it in Blender. $\endgroup$ – gig6 Apr 25 '20 at 17:37
  • $\begingroup$ Create a grayscale image. Following the settings he used, Black = transparent, white = opaque. Paint black where you want the masked video to be transparent, white where you want it to show, and gray if you want something in between. Some of the settings will be in different places in 2.8, but the overall process is the same $\endgroup$ – stphnl329 Apr 25 '20 at 18:16
  • $\begingroup$ That's the part I don't know how to do is "paint" the mask. Do you know where I can do this in Blender's video editor? $\endgroup$ – gig6 Apr 25 '20 at 20:21
  • $\begingroup$ You'll have to create a new image texture that is then used as the mask. You can do so using Blender's texture editor or external software. $\endgroup$ – stphnl329 Apr 25 '20 at 20:28
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In the movie clip editor (not the sequencer) you can create and animate masks.

enter image description here

In the VSE select the strip you want to overlay, add a "mask" strip modifier and select the mask you want to use. Then set the strip to use "alpha over" blend mode in the Adjust->Compositng settings for the strip.

The top strip will be overlayed on the bottom strip using the mask as alpha channel.

enter image description here

There is no need to create black and white images to be used as masks. The mask tools for blender are quite sophisticated.

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So my problem was that I wasn't aware that the mask had a start frame and end frame setting (in red). By default it was set to start at frame 1 and end at frame 100. I thought because I created the mask at frame 674 to frame 800 (in purple) that it would automatically be applied to those frames. As I scrubbed the video I could see the mask animate at the proper frames (from 674 to 800) so I thought I had done everything correctly. I upvoted susu's answer because that IS the correct way to apply a mask, which is exactly what I was doing, I just didn't have it set to the proper frames.

enter image description here

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