Our video thumbnails either do not appear, or sometimes show up for a second while the page loads and then disappear. A few of them show up persistently, but sometimes disappear for bit, until the page is refreshed.
Solved this by
mp4box -brand mp42:1 -add input.mp4 -new output.mp4
The ffmpeg output of the working video is:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'room1na/output-ben_room1_foot.mp4':
Metadata:
major_brand : mp42
minor_version : 1
compatible_brands: isommp42
creation_time : 2023-04-14T20:23:48.000000Z
Duration: 00:01:55.64, start: 0.000000, bitrate: 1580 kb/s
Stream #0:0[0x1](eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], 1580 kb/s, 15 fps, 15 tbr, 1000k tbn (default)
Metadata:
creation_time : 2023-03-09T21:46:28.000000Z
handler_name : VideoHandler
vendor_id : [0][0][0][0]