Requested feature overview description.
The first frame of some videos does not tell much about what the video is about. I suggest using either a time position of the video or an image post for the thumbnail.
Why would it be useful?
The thumbnail will give clues about what the video is about.
What part(s) of the site page(s) are affected?
Thumbnails for videos and flash animations. Pages of posts that use an image post thumbnail will link to the thumbnail post page. Edit and Upload will have a field for thumbnail post ID , time or frame number.

Something was just changed in the matrix.

BirdOfGrain said:
Something was just changed in the matrix.

https://en.wikipedia.org/wiki/False_memory#Mandela_Effect

Those suggestions for how this should be dealth with are bad because they could be extremely easily abused to give the posts even more misleading thumbnails. Also separate posts as thumbnails is bad idea because there is virtually no way to post thumbnails for videos without it being directly against like fifty different uploading guidelines.

Pakattu_suojakaasuun said:
Those suggestions for how this should be dealth with are bad because they could be extremely easily abused to give the posts even more misleading thumbnails.

Tags and ratings can already be abused. Rules for thumbnails should be added.

Pakattu_suojakaasuun said:
Also separate posts as thumbnails is bad idea because there is virtually no way to post thumbnails for videos without it being directly against like fifty different uploading guidelines.

post #1787730

There are zero_pictured posts.

post #2055584

Flash is already being deprecated, as in all the current files stay as download only and new files cannot be uploaded. So why waste development time on it now, especially when we are in somewhat hurry to get out of decade old codebase to new one: forum #279936

With videos, they already do not show the first frame, they show most representative frame out of first 100 frames (e.g. post #2107300 starts with black frame with watermark). GIFs show first frame and APNG either show first frame or deliberately inserted non-animated frame, example:
post #2051896

We already also have hundreds of regular images where thumbnail is not representing the content of the post, misleading_thumbnail.