@mryanmarkryan2 The feature for adding webm files as wallpapers is broken due to some upgrading of code. Hopefully, that will come back. And, hopefully mp4 supported will be added too.
For now though, the huge hassle way is:
Here's how you can convert an mp4 video to a webm file and zip it up so you can add it as an animated wallpaper:
Goto https://ffmpeg.zeranoe.com/builds/ and download ffmpeg to your desktop.
Extract the zip file to a folder and then rename the folder "ffmpeg".
Open a command prompt and run:
Move the mp4 you want to convert to the ffmpeg bin directory and rename the mp4 to "video.mp4"
Then, run this command:
ffmpeg -i video.mp4 -c:v libvpx -crf 30 -b:v 0 -an video.webm
Now you'll have the mp4 video as a webm video without audio as the file video.webm.
ffmpeg -i video.webm -vf "select=eq(n\,0)" -q:v 3 poster.jpg
Then, you'll have a pic of the first frame.
Then, create the following file in the bin folder (while filling in the info you want).
first frame image=poster.jpg
[Web UI Pages]
Then, zip up persona.ini, video.webm, and poster.jpg as background.zip. You can select the 3 files in Windows Explorer, right-click the selection, goto "Send to" and choose "Compressed (zipped) folder" to create the zip file if you want. Or, you can use a utility like 7-zip.
Then, in Opera, under Easy=setup, you just click "add wallpaper", switch to the directory background.zip is in, switch the filter drop-down to "Wallpaper archive" and open background.zip.
You can search Google for ffmpeg how-tos etc. if you need to do something more specific with the conversion.
Now, if you want to convert a webm file to an animated zip file an easier way than the above, you can have Opera 58 do it for you.
Download Opera 58, launch the installer, click "options", set "install path" to a folder named "Opera VBG" on your desktop, set "install for" to "standalone installation", uncheck "import data from default browser" and install.
In that Opera, add your webm file as a wallpaper and it'll be accepted as you'd expect. Then, close that Opera. Then, in the "Opera VBG\profile\data\themes" folder, you'll have a zip file for the video background that contains the proper stuff. You can then add that zip file as a background in newer versions of Opera and it'll work. It just won't have a poster in it. But, that's usually not a big deal. You could unzip it, add a poster and zip it back up though if you wanted to.