For the record, to get a video to properly play at the start - it currently needs to be
Video to be
- MP4 container
- 720p (1280 x 720)
- 25 FPS maximum
Audio to be MPEG AAC (mp4a) (48,000khz is fine)
That conversion can mostly be done using VLC. That’s what I used to convert from the UE4 LOGO intro given on the branding guidelines.