If you need to track start, 25% and 50% and 75% processes and end events of a Kaltura video player via GTM, create a GTM tag and paste the following script there:

<script>
    var script = document.createElement('script');
    script.onload = function () {
        if (  typeof kWidget !== 'undefined' && kWidget !== null ) {
            kWidget.addReadyCallback(function(playerId){
                var kdp=document.getElementById(playerId);

                kdp.kBind('firstPlay.fp',function(){
                    gtag('event', 'kaltura video player', {
                        'event_category' : 'video start'
                    });

                    kdp.kUnbind('.fp');
                });

                kdp.kBind('firstQuartile.1q',function(){
                    gtag('event', 'kaltura video player', {
                        'event_category' : 'video progress 25%'
                    });

                    kdp.kUnbind('.1q');
                });

                kdp.kBind('secondQuartile.2q',function(){
                    gtag('event', 'kaltura video player', {
                        'event_category' : 'video progress 50%'
                    });

                    kdp.kUnbind('.2q');
                });

                kdp.kBind('thirdQuartile.3q',function(){
                    gtag('event', 'kaltura video player', {
                        'event_category' : 'video progress 75%'
                    });

                    kdp.kUnbind('.3q');
                });

                kdp.kBind('playerPlayEnd.pe',function() {
                    gtag('event', 'kaltura video player', {
                        'event_category' : 'video end'
                    });

                    kdp.kUnbind('.pe');
                });
            });
        }
    };
    script.src = 'http://cdnapi.kaltura.com/p/{partner_id}/sp/{partnerId}00/embedIframeJs/uiconf_id/{uiconf_id}/partner_id/{partnerId}';
    document.head.appendChild(script);
</script>

Replace {partnerId} and {uiconf_id} with the partner ID and uiconf ID of the video player account.