The thumbnail is the poster that appears in the player window before video playback begins.
This endpoint allows you to upload an image for the thumbnail.
To select a still frame from the video using a time stamp, use Pick a Thumbnail to pick a time in the video.
Note: There may be a short delay before the new thumbnail is delivered to our CDN.
Tutorials using Thumbnail upload.
Add a Body parameter for the thumbnail file, and specify it's mime requirements(jpeg).