Video Format
fm
Initiates the Short-Form Video feature and allows you to specify the video format. fm=mp4 is required to use most of the Short-Form Video parameters.
The following formats are supported:
mp4: Required for Short-Form Video. MP4 is the most widely supported video format compatible with most browsers and devices.json: Outputs the video metadata as JSON
The video-thumbnail modifies the accepted value list. Check the video-thumbnail documentation for more information.