Video’s dont auto play at mobile.  You have to update the query parameters to force it to auto play, and even then some browsers don’t support it. Most people use a fall back image at mobile.

Joe

how can i do the fall back image thingy ?

Hey there!

A fall back image is just an image that you load as a regular background image. To achieve this, you can upload the background image as seen in this screenshot:

You can choose any image you’d like, it can be completely different from your video if you’d like. But keep in mind, when you make changes to your mobile view, these changes will be applied to your desktop page. To make changes to mobile without effecting desktop – hold down Command if you’re using a Mac, or hold down Control if you’re using a PC. 

Here’s some handy documentation about it: http://documentation.unbounce.com/hc/en-us/articles/203788184-Working-With-the-Page-Builder-

Hope that helps!

PS - I love your use of the word “thingy”, that’s one of my favourite filler words.