Answers.Body: <p>If you prefer a free editor, <a href="https://www.blender.org/" rel="nofollow noreferrer">Blender</a> could achieve something like this. You need to look at the <a href="https://docs.blender.org/manual/en/latest/compositing/types/matte/luminance_key.html" rel="nofollow noreferrer">luma key nodes</a>.</p>
  
  <p><a href="https://www.blender.org/" rel="nofollow noreferrer">Blender</a> is free but has a steep learning curve. Adobe Premiere could do this quickly using a <a href="https://helpx.adobe.com/premiere-pro/how-to/add-track-matte-key.html" rel="nofollow noreferrer">track matte</a>, but it's not free.</p>
  
  <p>After Effects is also paid-software, and has a steeper learning curve than Premiere, but can also use track mattes - see the other answer for details.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-06-10T21:24:15.303Z
Answers.Text: Thank you, I'll give Blender a try.
Answers.UserDisplayName: Lopsi
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-06-10T12:28:49.380Z
Answers.LastActivityDate: 2020-06-10T12:28:49.380Z
Answers.UserDisplayName: tomh
Answers.Body: <p>This would be easy to do with After-Effects. Do the following:</p>
  
  <p>Create a new composition with the settings of the mp4. You can drag it on the composition symbol to automatically create it.</p>
  
  <p>Then, drag your alpha-mp4 above the color-mp4. Now, set the "track matte" to "Luma-Mask" from the alpha-mp4. This should be all.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-06-10T00:35:59.310Z
Answers.Text: Thank you, I'll try it out once I have the After Effect.
Answers.UserDisplayName: Lopsi
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-06-09T13:25:18.893Z
Answers.LastActivityDate: 2020-06-09T13:25:18.893Z
Answers.UserDisplayName: Florian Claaßen
Body: <p>A noob question. I have two mp4 video files. The first one is ordinary color video (right side). </p>
  
  <p>The second one is transparency mask video (alpha), it's a mp4 video not an image (left side). 
  This second video has gray-scale colors, and it changes frame by frame. This second video has no alpha channel. </p>
  
  <p><a href="https://i.sstatic.net/ntys1.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ntys1.jpg" alt="enter image description here"></a></p>
  
  <p>What video editor is able to mask the first color video with the second alpha video, so that the first video is rendered with its transparency changing frame by frame according to the second alpha video? And please a short explanation on how to do it? </p>
  
  <p>I prefer a free editor, but if there isn't one, a proprietary editor doesn't matter. 
  Thank you. </p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-06-09T13:29:03.877Z
Comments.Text: Are you using a Mac or a PC?
Comments.UserDisplayName: tomh
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-06-10T00:32:40.870Z
Comments.Text: @tomh I'm using a PC
Comments.UserDisplayName: Lopsi
Tags: <video-editor><mask><alpha>
Title: How to mask a mp4 video with another alpha mp4 video
UserDisplayName: Lopsi
ThreadText: # How to mask a mp4 video with another alpha mp4 video
  
  (Asked by: username_0 on 2020-06-06)
  
  A noob question. I have two mp4 video files. The first one is ordinary color video (right side).
  
  The second one is transparency mask video (alpha), it's a mp4 video not an image (left side).
  This second video has gray-scale colors, and it changes frame by frame. This second video has no alpha channel.
  
  [![enter image description here](https://i.sstatic.net/ntys1.jpg)](https://i.sstatic.net/ntys1.jpg)
  
  What video editor is able to mask the first color video with the second alpha video, so that the first video is rendered with its transparency changing frame by frame according to the second alpha video? And please a short explanation on how to do it?
  
  I prefer a free editor, but if there isn't one, a proprietary editor doesn't matter.
  Thank you.
  
  **Tags:** video-editor, mask, alpha
  
  > **Comments:**
  > **username_1**: Are you using a Mac or a PC?  
  > **username_0**: @username_1 I'm using a PC  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_1 on 2020-06-10. Score: 0 | Accepted answer
  
  If you prefer a free editor, [Blender](https://www.blender.org/) could achieve something like this. You need to look at the [luma key nodes](https://docs.blender.org/manual/en/latest/compositing/types/matte/luminance_key.html).
  
  [Blender](https://www.blender.org/) is free but has a steep learning curve. Adobe Premiere could do this quickly using a [track matte](https://helpx.adobe.com/premiere-pro/how-to/add-track-matte-key.html), but it's not free.
  
  After Effects is also paid-software, and has a steeper learning curve than Premiere, but can also use track mattes - see the other answer for details.
  
  > **Comments:**
  > **username_0**: Thank you, I'll give Blender a try.  
  
  ---
  
  ### Answer by username_2 on 2020-06-09. Score: 0
  
  This would be easy to do with After-Effects. Do the following:
  
  Create a new composition with the settings of the mp4. You can drag it on the composition symbol to automatically create it.
  
  Then, drag your alpha-mp4 above the color-mp4. Now, set the "track matte" to "Luma-Mask" from the alpha-mp4. This should be all.
  
  > **Comments:**
  > **username_0**: Thank you, I'll try it out once I have the After Effect.  
  
  ---
  
  