Related to Martin's video at: https://hq.moodle.com/mod/forum/discuss.php?d=1808
The original one was in 4K resolution with HEVC codec. It cannot be played on Chrome, Firefox. For some users, they only get the audio, not the video.
Martin's had to reduce the resolution to 720p and now it can be played.
Note: The original file played well with Safari on MacOS.