You are diligently creating tutorials in a short time; very impressive 
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This is a very nice effect which can be used as an inspiration for another way to overlay two videos.
Cool, but there are a lot of white alias artifacts on the inside edges of the LONDON text. I wonder if this is due to using Chroma Key and can be avoided using a PNG with alpha. Shotcut does not export PNG with alpha, but you can either create the text in another program or export a short or single frame video using an alpha preset.
Yes, I noticed that. Here’s an enlarged screenshot from youtube. Artefacts especially noticeable on the O and D curves:
I imported the png from Shotcut into GIMP, selected the white middle part and deleted it then put a blue layer behind it and it also gave me lots of artefacts:
… but I’d have to Chroma-key out the white middle text first to do that wouldn’t I?
What tool did you use to delete the white filling? I tried to delete it in paint.net which works if I use the magic wand with a high tolerance (Threshold in Gimp).
I selected the “select by colour” tool in GIMP and hit delete. But I just remembered that if I choose “Grow” (- by 2 pixels)… it gives a much better result.
I was thinking along the lines of inverting the alpha channel before saving it as PNG or video with alpha rather than selecting by color and removing. Shotcut has the filter Alpha Channel: Adjust that can invert as well as grow.
Great tutorial @jonray but I think you have a couple of extra steps. Reproduced your text with flag. Created a new project. Made a 10 sec green color clip. Added text and put it on a V3. Used chroma key advanced to key out the white.
Set the filter to hue-chroma-intensity. Set the intensity parameter to 50%. Slope to 20%. That eliminates virtually all the artifacts. Added the flag video to V2… Saved the project as Berlin text.
Created a new project. Added the Berlin image to V2. Opened the Berlin text project as an XML MLT clip. Put the clip on V3. Added a chroma key simple filter. Then exported with interpolation set to Hyper/ Lanczos.
Wow, @samth, @shotcut and @sauron, that’s all great advice. Just when I thought I knew a bit about chroma-keying…
There’s lots there I didn’t know about. Yes, @sauron - much better result than mine. (You just need Beethoven’s “Ode to Joy” from Symphony No. 9 in the background …) I’ll have another go at my London version when I get some time. Thanks for the tips, I’ve learned a lot!
That is quite the improvement . I searched for an explanation of the “Chroma Key: Advanced” filter but unfortunately there is none. Definitely a necessary part of the newly begun documentation category.
The Chroma Key: Advanced filter is actually the frei0r: select0r filter. The documentation for the parameters can be found here:
Hi @sauron, I re-made the London title using your method:
Also here’s a comparison video -top:original, bottom: using chroma-key:advanced. (Note: completely different timings of the animated text and background). I’ve paused the middle part with an exported frame so they can be compared directly:
Interesting… although I seem to have lost the dark text border though on the 2nd version!!
Settings for the chroma-key:advanced filter:
Thanks as well.
A link to this in the documentation category would be helpful and would reduce the work to explain each filter.
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The outline alpha channel defaults to 170. I noticed that my outline was light. Changed the alpha to 255.
Ah, thanks @sauron, very helpful - actually I remember this came up very recently in @drm’s post (No.10 on the list):
https://forum.shotcut.org/t/v19-08-beta-now-available/12358/3
Now it makes more sense to me - because my London text with pink background was an exported PNG directly from SC. I just tested the border colour in GIMP (shift+eyedropper):
…so the border is not black, but a deep purple*. I must remember to change the alpha to 255 if I want to have a solid black border.
Interestingly as well, on close-up, half the border seems to be grey. I wonder why this is so?
(*Deep Purple - now I reckon that would be a great name for a rock group…
!!! )
Tried @shotcut’s suggestion to use Alpha Channel Adjust filter. It works very well.
This is using Chroma Key Simple with default distance of 28.8% and Alpha channel adjust with Mode set to Shrink Soft with Amount set to 23%.
This is just using Chroma Key Simple at default setting.
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Nice technique! Thanks Sauron, cool cool COOL! 
Very very quick demo using chroma-key:simple and alpha adjust. Also, crucially, setting the border to alpha = 255. I would vote, I think, for @drm’s suggestion of making the border alpha 255 by default - I think users would expect a text border to be solid? Certainly gave me some confusion and frustration!
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thanks a lot, that’s what I was looking for!
Just a thought on the artifacts from Gimp and other raster image editors. Inkscape, a FOSS vector based editor, affords the option to export the image as a PNG. From this source, the artifacts are less likely to creep into the works.