Hi @razvan_iacob,
I see you're using an older version of the player [v2.45]. Can you try creating a new player with the latest [v2.51] and see if that works? In addition, since version 2.48, the default playback method is HLS rather than progressive download, which is what your current embed code is using, for video clips longer than just a few seconds, this provides an advantage as HLS allows for adaptive bitrate. Assuming you're not using external CDNs, HLS is achieved via the kaltura-nginx package which includes the nginx-vod-module. What CE version are you currently using?