Video Quality issue

Your original video was probably shot at around 50 - 100mbps whereas your edited video was exported at a mere 10mbps which is why it shows far more artefacts than the original.

If you exported it at 50mbps or more it would be identical to the original footage but it probably wouldn't work on YouTube.

As I mentioned earlier the degradation is minuscule and appears to be the natural result of shooting violent movement at 200kbps and exporting at 10kbps.

If you haven't done it already, you could try optimising your media to ProRes 422 during editing and then export it using H.264

Another thing to be aware of when comparing video clips is to ensure you are examining the same frame as the quality can vary from frame to frame.

So you could be viewing a frame that looks fine and the next one could be poorer.

Yet another possibility is that when you are editing, you are watching the image in the Viewer which by its nature is comparatively small and gives the illusion of a brilliant image.

The final video is usually viewed full-screen which naturally makes any blemishes more obvious.

The Data Rate is critical.

I have found anything below 1200 and the image starts to fall apart. Try a 64 just for laughs.

You are using 4K HEVC So you have to find the sweet spot between file size and quality.

Al

Please give complete details of your original media specifications. Please give your project and export settings. Please post screenshots of before and after.

I can't see your video as it is "Private".

I can't see any significant difference between the 2 screenshots.

Al has probably got it. 10,000kbps is perfectly fine for 1080p but it is cutting it fine with 4K.

Try a test with nudging up the bit rate to around 1500-2000 kbps.

Al

Just checked up on your camera and seen that it shoots 4K at 200mbps so exporting at 10mbps is going to display a tremendous reduction in quality on anything that is in motion.

It's a minor miracle that it looks as good as it does.

Where is the lower quality being seen?

In the FCP Viewer during Timeline playback or after an export from FCP?

Al

What's the difference between the second and third image? They look like Compressor presets. The FCP project is 60fps, but Compressor is changing it to 59.94. Is that what you want to do? What's the original media?

The two images don't show significant change when compared at the same size. The output is slightly softer, which might be due to the speed change and codec/bit rate change. Haven't seen the specs of the original from the QT player.

I can see nothing wrong with the processing. The footage has so much violent movement that it is going to exhibit some pixellation and artefacts.

I'm surprised there isn't more.

That's not to be taken as a criticism of your filming as I know how hard it is to capture smoothly an airliner travelling in a straight line. You did remarkably well capturing such aerobatic manoeuvres.