Native containers vs remux-first formats
Mp4 to gif, webm to gif, and mov to gif natively
Mp4 to gif / convert mp4 to gif / make gif from mp4 / create gif from mp4 work directly. Webm to gif / convert webm to gif and mov to gif / convert mov to gif (QuickTime) are likewise native. Screen recording to gif works only when you upload the recording file.
Avi to gif, mkv to gif, m4v to gif — remux first
Avi to gif / convert avi to gif, mkv to gif / convert mkv to gif, and m4v to gif / convert m4v to gif are honest remux/convert-to-MP4 locally, then upload the MP4 file. We do not claim in-browser demux for every container.
No YouTube or Twitch URL→GIF
Paste-a-link is unsupported. Download/export the clip yourself, then convert video to gif from the file. Twitch clips and YouTube URLs are out of scope.