Found this in your other 'preview' thread:
>I created an App Preview using iMovie 10.1.12 on MacOS Catalina 10.15 Beta
>length 00:00 / 00:04
>filesize 1.4MB file-format .mp4
Requirements are minimum length of 15 seconds... Just 4 is a problem, I think, and the first one I'd correct.
Confirm your process to add a soundtrack here: Creating App Previews with iMovie
Use iMovie to check the info on that clip and see details on the audio.
- Codec: 256kbps AAC
- Sample Rate: 44.1kHz or 48kHz
- All tracks should be enabled
- 1 track with 2-channel stereo (1st channel L and 2nd channel R)
- 2 tracks with 1-channel stereo (1st track L and 2nd track R)
Thank you KMT, I have now uploaded a good App preview.