First, start by installing yt-dlp to download the YouTube video: https://github.com/yt-dlp/yt-dlp
Secondly, install ffmpeg because you’ll need to re-encode the video to libx264: https://ffmpeg.org/download.html
Next, find a YouTube video and download only the first 30 minutes of it at 720p resolution with no audio using yt-dlp:
yt-dlp -f "bestvideo[height=720]" --download-sections "*00:00:00-00:30:00" https://www.youtube.com/watch?v=lWLUJHtlYyM
Microsoft Teams backgrounds are stored in the following %localappdata% path:
C:\Users\<username>\AppData\Local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams\Backgrounds
The Teams UI will not detect your new video if you simply drop it into this directory. You must rename it to match one of the four existing .mp4 files:
feelingDreamy2Animated_v=0.1.mp4
feelingDreamy4Animated_v=0.1.mp4
feelingDreamy5Animated_v=0.2.mp4
feelingDreamy7Animated_v=0.1.mp4
After renaming, you need to re-encode it to libx264 using ffmpeg:
ffmpeg -i feelingDreamy4Animated_v=0.1.mp4 -c:v libx264 -crf 23 -preset medium -c:a copy feelingDreamy4Animated_v=0.1.mp4
Once the video has been renamed and re-encoded, it should appear and work as a selectable background in Microsoft Teams.