Because I want to keep the original embed form from Oxwall without modification.
And I like your suggestion, I will add the feature of "edit thumbnail" for any video into the roadmap. So stay tuned for next release.
I think I will keep the original form original :) and then add a button for users to edit the video clip thumbnail when adding video completed. How would you think?
Thanks for considering my suggestion ;)
Is it something I could manually edit in the embed code?
For reference:
http://stackoverflow.com/questions/2068344/how-do-i-get-a-youtube-video-thumbnail-from-the-youtube-api