With the free and open-source 3D computer graphics software program Blender it is easily possible to create short animations from images extracted from GMSH. Although the program is much more powerful it is suitable for our purpose.

Download, install and open the program.

On the left bottom side click on the cube icon and open the Video Sequence Editor.

Click on Add and Image to choose the images extracted from GMSH.

Navigate to the folder where the images are located and select them simply by making multiple selection boxes (hold left mouse button and drag). Now you have to edit the box in the lower left corner and adjust the start and end frame to your case.

Then you have to open the render menu on the right by clicking on the camera symbol. Now the dimensions of the animation have to be set. Depending on the resolution of your images edit the X and Y value and set the percentage to 100. In the frame range you should use the same values as in step 3. The frame rate namely the images shown per second you can adapt to your means, nevertheless a value of 5 is a good starting point.

Now the output path and the file format have to be set. For the file format H.264 is a good choice and you should select RGB for a coloured animation. In the encoding menu also select H.264 as the format.

That's it, if you now click on Animation in the render menu your video is created.