How do I upscale an iOS App Preview video to 1080 x 1920?

Finally, ffmpeg -i input.mp4 -acodec copy -crf 12 -vf scale=1080:1920,setsar=1:1 output.mp4 did the trick!

Turns out that ffmpeg tries to be smart about aspect ratio, so that the actual size is 1079x1920 with an aspect ratio of 2000:2001.

• setsar=1:1 forces an aspect ratio of 1:1 and hence, the right resolution
• -crf 12 as desired quality roughly results in the same file size as the original file created by iMovie, so it should be a safe bet bit rate-wise

I already answered to the same question here (solution using iMovie 10): https://stackoverflow.com/a/51118682/521316

I used Video resize https://itunes.apple.com/us/app/video-resize/id1073693347?mt=12 from the Mac App Store to resize the video. Quickly did the work but the resolution was off. Started a new App Preview in iMovie, Imported the newly resized video, trimmed it down to about 1 second, added the original video I had resized, trimmed clip video to 30secs, Share -> App Preview -> video size now at 1080x1920. Crossing fingers it will be accepted