I'm having trouble uploading App Previews in App Store Connect. Despite following all of Apple's specifications, App Store Connect rejects the file with messages like:
This happens either as soon as I start uploading the file or after it has finished processing.
It also happens for both supported formats: H.264 and ProRes 422 (HQ). I have tried using about 10 different export presets for the file, and even tried re-converting my (already compliant) video editor output with ffmpeg, but no luck.
AppStore Connect often gives the wrong error message (as of March 2021). First, make sure that:
Once you know the above is not the problem, I recommend going with iMovie export (official docs). iMovie is free, comes with every Mac, and has a built-in App Preview export capability.
Whatever you use for editing your App Preview (Premiere, After Effects, HitFilm, etc.), export the video in high (maybe even lossless) quality.
Open iMovie.
File > New App Preview.
Drag & drop your video file into the iMovie window, and then into the timeline.
Click the export icon (hidden in the top right corner of the iMovie window)
Select "App Preview"
Export the video
It's unclear to me how exactly iMovie encodes the video, but it works.