You can use the snapshot feature of Wondershare Filmii’s Advanced Editing mode to capture a PNG image. This is a great way to capture a thumbnail for a YouTube video.
Move the red playhead in your timeline to a frame you’d like to save and then click the camera icon under the video preview. The frame displayed in the preview will be saved to your computer as a PNG and it will also be added to your media library so you can easily drag it into your timeline if you like.
After you take a snapshot, an option will appear to click if you want to use your snapshot as a YouTube thumbnail. If you click this option then the snapshot you took will show up as the recommended thumbnail if you upload directly to YouTube from Filmii.