This was mostly done using Adobe After Effects, using a photograph by Steve Halama from the Unsplash website.
Initially working in Adobe Photoshop, I separated the main character, the sky and the ground using duplicate layers - each one masked to hold only their key part of the picture.
Using the Context aware fill in Photoshop, I generated the part of the sky obscured by the central figure.
Then in After Effects, I imported this Photoshop layered file and created a composition. I increased the scale of the sky significantly, which gave me room to animate some movement.
Using the CC Slant effect on this enlarged sky, first I grounded the effect on the top of the foreground level. I then keyframed the slant effect as much as I could on the left, then moved forward in time and created another keyframe as far as I could on the right.
Obviously this 20 second composition wouldn't loop. So I created a main 35 second composition, and added my 20 second animation into that. I chose a split point and cut the composition in 2, which then I can use as a looping beginning and end - as these are contiguous frames. The footage to the right of the cut becomes the beginning of the clip, the footage on the left is dragged to the end.
But prior to this split, I duplicated the footage to provide the extra 15 seconds or so in the middle. By carefully keyframing the opacity of these (fading out one and fading in the duplicate - and doing the opposite with the end clip), the eye is not distracted unduly.
A logo and some particles floating in the generated sky movement direction, just add finishing touches along with colour corrections via adjustment layers.