JS Team!!!
Here lift you images about my problem.
1. On mobiles video thumbails not fill all the space.
2. When i press play, nothing heppend, just bigger image...
Solution?
THANK YOU!

Hi,

there was wrong custom css code at /templates/socialize/css/custom.css line 32

 .joms-media__thumbnail {
    height: 200px;
    width: 250px;
 }

@media screen and (min-width: 480px) {
  .joms-media__thumbnail {
    min-height: 200px;
    min-width: 250px;
  }
}

Albertus, many thanks :-)