user1175: I'm a newbie in video editing. Here's what I do:

I record the screen of my phone, explaining some stuff
Video is recorded in portrait mode, thus it's a vertical video
I edit this video by adding some pictures or audio effects and post it
However, the video is vertical and added pictures block the real captured phone screen

Here's what I want to do:

Recording the screen just like before
Somehow shift this vertical video to the left of a new video
Add pictures and other marks to the right in the editing process
Export the whole as a square video

In fact, I want to do this:

I don't know what keywords should I use in search to find guidelines on how to do this. I don't know what software (preferably free and open source) can I use for this. I'm stuck at this point. Can anyone help?

user30165: A great free online editing software is WeVideo. In WeVideo, any video that doesn't take up the whole screen (like video shot in portrait mode) can be layered on top of any other video by putting the video you want on top by putting that video on the video track above the video you want below it. The way to get your video to look that way you want it to would be to have the blue square with the words on in Video track 2, and the black background and lightning bolt on the lower track. Then, you could double click on the blue box clip, and it should bring you to the transform menu  where you can drag the clip that you have selected around until it is where you want it in the little preview screen. This way you can have the clip in the second track be anywhere in the screen. Hope this was helpful!

1175: <p>I'm a newbie in video editing. Here's what I do:</p>

<ul>
<li>I record the screen of my phone, explaining some stuff</li>
<li>Video is recorded in portrait mode, thus it's a vertical video</li>
<li>I edit this video by adding some pictures or audio effects and post it</li>
<li>However, the video is vertical and added pictures block the real captured phone screen</li>
</ul>

<p>Here's what I want to do:</p>

<ul>
<li>Recording the screen just like before</li>
<li>Somehow shift this vertical video to the left of a new video</li>
<li>Add pictures and other marks to the right in the editing process</li>
<li>Export the whole as a square video</li>
</ul>

<p>In fact, I want to do this:</p>

<p><a href="https://i.stack.imgur.com/Q8YVp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Q8YVp.png" alt="enter image description here"></a></p>

<p>I don't know what keywords should I use in search to find guidelines on how to do this. I don't know what software (preferably free and open source) can I use for this. I'm stuck at this point. Can anyone help?</p>
 30165: <p>A great free online editing software is WeVideo. In WeVideo, any video that doesn't take up the whole screen (like video shot in portrait mode) can be layered on top of any other video by putting the video you want on top by putting that video on the video track above the video you want below it<a href="https://i.stack.imgur.com/bVFFs.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bVFFs.jpg" alt="as can be seen here"></a>. The way to get your video to look that way you want it to would be to have the blue square with the words on in Video track 2, and the black background and lightning bolt on the lower track. Then, you could double click on the blue box clip, and it should bring you to the transform menu <a href="https://i.stack.imgur.com/VoxaJ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VoxaJ.jpg" alt="this menu"></a> where you can drag the clip that you have selected around until it is where you want it in the little preview screen. This way you can have the clip in the second track be anywhere in the screen. Hope this was helpful!</p>
