Problem uploading webm

I was trying to upload this video (https://twitter.com/justscoobydoo/status/1082435928730357761) which I got via savetweetvid.com (specifically the DL site gives me a mp4 and I just changed the file extension) but only get an error 500 back.  
Maybe there are some special requirements for webms that I don’t know about.

Well that’s your problem right there. Use some online converter or VLC to turn the mp4 into an actual webm, because the difference isn’t just the file extension name.

@The Smiling Pony  
I thought they shared the same container format, isn’t that why renaming is enough for video players?

@rannius  
Only if they were named wrong in the first place.
 
Also are you the same guy nyama came to be about with literally the exact same problem of trying to upload an mp4 with a webm extension?
 
How do so many people make this mistake? istg.

@ZippySqrl  
Because people are used to the renaming trick (like me) and don’t know enough about video formats (like me).

@The Smiling Pony  
ant thanks, it worked with proper converting