I have a tip for those who would like to display a thumbnail on mobile devices without the need for ffmpeg or for the user to upload an image, add the following codes in the files "video.phtml" and "videojs.phtml" (themes / wowonder / layout / players /):

- In the "video" tag change the preload = "auto" property to preload = "metadata".

- Right after, in the "source" tags, inside SRC, before closing quotes, add # t = 0.05 or the desired time in place of "0.05".