From the github tracker, i got this suggestion. Seems to work very nice:
/* these elements are problematic with transform:scale */
.scaledstuff .vjs-progress-control { pointer-events:none; }
.scaledstuff .vjs-progress-control:before {
background-color: rgb(0, 0, 0); content: '';
height: 100%; width: 100%; pointer-events: auto;
}
.scaledstuff .vjs-volume-control { display:none; }
/* but work fullscreen */
.scaledstuff .vjs-fullscreen .vjs-progress-control { pointer-events:auto; }
.scaledstuff .vjs-fullscreen .vjs-progress-control:before { display:none; }
.scaledstuff .vjs-fullscreen .vjs-volume-control { display:block; }