By far, there are certainly thousands of screen captures taken directly from existing videos on the site. Tens of thousands, perhaps. Currently on the first page of the recently posted items (which displays 100 for me), at least 10 are screen captures. That's 10%. It's not unreasonable to believe they are contributing 5-10% of the site's total content. Shouldn't these be discouraged, and rather the original video be uploaded instead? If it's a matter of technical competence... well users have figured out how to upload files from Instagram, they can also figure out just as easily how to cut a video down to a 25 MB clip to upload here. Laziness shouldn't be rewarded, and it is only cluttering the site with sub-standard quality content.
Generally speaking videos are preferred over screencaps. One exception would be if the video is long or unfocused. Sometimes it can be the case that a video is pretty mediocre as a whole but one or two screenshots of it are great. And of course there are cases when the video isn't available (i.e., the uploader found the screenshot somewhere but it didn't come with a video) in which case I'd rather have people upload the screenshot than nothing at all.
These are the exceptions of course, and as you well know we will happily merge screenshots into the video most of the time.
I actually prefer screen caps. Makes sense to me when I go through a 45 second video clip; as one example; and find that only a few seconds are worth looking at.
To each their own. Interviews come to mind where many would prefer the screen cap. If she flexes for a second but is just standing there the rest of the time, then it makes total sense. Screen caps of lifting and flexing vids, though? I would definitely prefer the video.
Yeah, there's one user in particular who used to be pretty bad with uploading multiple screenshots for short clips, he's gotten way better after being asked to knock it off and mostly uploads the actual videos now. I'm still meaning to go back and replace a bunch of his previous screencaps with video at some point.
I've also found that uploading the relevant video clip and having their screencaps merged into it is a good way to discourage people from doing that, maybe with also dropping them a link to this thread so that any editing they do on the videos will be lossless.