Thumbnails / Video preview not working for videos longer than 1 second

Nextcloud version: 20.0.6
Using docker: nextcloud:fpm-alpine
Caddy reverse proxy (v2.3.0 h1)
PHP version: 7.4.14

I am new to nextcloud and just set up a instance with a primary object storage.
The issue i am facing is that i see no previews for video files except when they are very short. I’ve followed: Nextcloud: Install Preview Generator –

/var/www/html/occ preview:generate-all -vvv
Seems to work, it lists all the mp4 files as it should.

It seems like running the generate-all command has not effect at all, the one video that has preview has it the minute i uploaded it (might have been generated on demand).

Any help will be much appreciated.
Also, please tell me if more logs are necessary or if there is a special debug/verbosity flag i should use.

Quick update, trying to keep on and understanding what happens I’ve figured that:
first, the MP4 preview provider does not exists and Movie should take care of all the video content. Another thing is that the ffmpeg command at

fails for the specific files with an error:

[mov,mp4,m4a,3gp,3g2,mj2 @ ...] moov atom not found
/tmp/oc_tmp_ecpDfD: Invalid data found when processing input

files are mp4 files. The files that succeed use a different provider surprisingly maybe because they are just 1 sec long.
The reason I didn’t see any error previously is that the previewgenerator app fails silently at: (Yes, you should log that).

Further examining the files shows that they are all of the same size of 15728640 (15.0M) although some of the videos I’ve uploaded are only 10M, which means they aren’t just cropped or uploaded incorrectly (viewing works fine).
I figure it has something to do with the s3 object storage.

If anyone has any help he can offer it will be much appreciated.
I will continue to look into it and keep this post updated.

Figured it out, hope this will help the next guy.
It is pretty simple looking at the code.
The movie preview generator only uses the first 5M (at least according to the code, no idea yet as to why the tmp files are 15.0M) of a movie when it is not stored locally (object storage in my case), I guess this is not enough to generate the preview for some movie, I will continue the discussion over a fix within the open issue in the git and will hopefully fix it sometime soon.