I'm trying to achieve the merging of multiple video strips like in the following 15 sec in, to 16 sec in - caravan to boat clip. I think the clip has been animated with a vertical strip.

  • Could this animated area be achieved with masks in Blender?

  • If so, how would I go about achieving an animated visible video area, over another video?

  • $\begingroup$ It can be done in blender... whether you will appear sane at the other end is questionable :P. After effects/final cut pro would be much better for this. $\endgroup$ Commented Sep 4, 2014 at 15:05
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    $\begingroup$ unfortunately I don't have after effects/final cut pro. How can it be done in Blender? $\endgroup$
    – reggie
    Commented Sep 4, 2014 at 15:35

2 Answers 2


There are a couple ways, but I would use masks:

enter image description here

  1. With a strip selected, add a mask modifier in the properties region (N) by pressing Add strip modifier > Mask. I also like to set the alpha blending to alpha over:

    enter image description here

    You can either use another strip to control the selected strip's alpha channel. You could use a scene strip to generate such a map based on the render output of a scene, or you could use an animated mask.

  2. To create a mask, use the UV/image editor with the mode set to mask. Press ⇧ ShiftA and select the type of mask to create.

  3. To animate it, transform it with G (translate) S (scale) and R (rotate). Insert keyframes with I.

    To move the keyframes around/delete them, you can use the dopesheet in mask mode:

    enter image description here

Unfortunately there doesn't seem to be any way to get the image editor to update in realtime at the moment, so you'll have to manually refresh it by pressing F12. For that to work, the viewed image must be set to Render result.


  • $\begingroup$ I've figured out how to animate the masks in the movie editor, but is there a way to see the key frames in the graph editor? I'm struggling to accurately move the keyframes around and sync them to my video strips. Is there a tutorial any-ware on how to accurately position key frames in the movie clip editor? $\endgroup$
    – reggie
    Commented Sep 5, 2014 at 15:39
  • $\begingroup$ In the VSE you can Add->Mask->MaskName - the list of masks are those created in the movie editor. $\endgroup$
    – sambler
    Commented Sep 5, 2014 at 17:38
  • $\begingroup$ In the UV image editor you can keyframe masks by pressing I. See the wiki for more info: wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.64/…. I don't have time to atm, but I'll update my answer with more detail.. $\endgroup$
    – gandalf3
    Commented Sep 5, 2014 at 17:45
  • $\begingroup$ Good question, great answer $\endgroup$
    – Nikos_VSE
    Commented Sep 6, 2014 at 6:40
  • $\begingroup$ good answer and you've trumped my up coming tutorial. $\endgroup$
    – 3pointedit
    Commented Sep 7, 2014 at 23:16

As well as keyframing masks you can get a lot of control by making your own animated video strip and using it as a mask strip. CGCookie has a archived tutorial that covers making and using the mask video. The only other tutorial I know of is by David McSween, he uses a single greyscale image and animates the brightness and contrast to get the transition.

The basics of creating an animated video to use as a mask is to create a video that defines the transition, black shows the old strip, white shows the new strip with levels of grey a mixture of the two. You can easily imagine using blender to create a simple animation of shapes for this, add this transition video as a strip in the VSE and then add a mask modifier and select the transition strip.


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