OK, I went through your video clip yet again... not the best way of describing the issue
but I now see you seem to be trying to display the same clip from the same source node to multiple "dashboard users".
I was able to do that, at least with my posted example... using separate browser windows, seperate PCs and even the RPi browser, just a bit slowly there.
However, I did find it better to have a separate node for the URL and include an inject or "start" button for the dashboard for "individual user" control of starting the videos in their browsers.
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\n })(scope); \n</script>\n\n\n\n","storeOutMessages":false,"fwdInMessages":true,"resendOnRefresh":false,"templateScope":"local","x":700,"y":340,"wires":[[]]},{"id":"7b44ef2ce3352db2","type":"function","z":"ef43236e7e19eab5","name":"","func":"msg.payload = \"http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/TearsOfSteel.mp4\"\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":520,"y":340,"wires":[["fbe4857646afebc2"]]},{"id":"1d682a1020aeb471","type":"ui_template","z":"ef43236e7e19eab5","group":"58ab9f631d25d819","name":"Vid_screen_3","order":1,"width":8,"height":4,"format":"<div>\n <video id=\"video4\" width=\"100%\" heigth=\"100%\"></video>\n</div>\n\n<script> \n (function(scope) {\n // Watch for messages being send to this template node\n scope.$watch('msg', function (msg) { \n if (msg) {\n\n var video4 = document.getElementById('video4');\n video4.src = msg.payload;\n video4.play();\n } \n }); \n })(scope); \n</script>\n\n\n\n","storeOutMessages":false,"fwdInMessages":true,"resendOnRefresh":false,"templateScope":"local","x":700,"y":380,"wires":[[]]},{"id":"7c1a4134b2d3a215","type":"function","z":"ef43236e7e19eab5","name":"","func":"msg.payload = \"http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4\"\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":520,"y":380,"wires":[["1d682a1020aeb471"]]},{"id":"b91f4371f84bbfe8","type":"ui_button","z":"ef43236e7e19eab5","name":"","group":"0f543f3af487dbc2","order":0,"width":0,"height":0,"passthru":false,"label":"Start","tooltip":"","color":"","bgcolor":"","icon":"","payload":"","payloadType":"str","topic":"topic","topicType":"msg","x":370,"y":260,"wires":[["2caf0d1f0b97a4b1"]]},{"id":"b6e78d551ec45606","type":"ui_button","z":"ef43236e7e19eab5","name":"","group":"0436fb6b71c7e33a","order":0,"width":0,"height":0,"passthru":false,"label":"Start","tooltip":"","color":"","bgcolor":"","icon":"","payload":"","payloadType":"str","topic":"topic","topicType":"msg","x":370,"y":340,"wires":[["7b44ef2ce3352db2"]]},{"id":"44a8db67d3a4b226","type":"ui_button","z":"ef43236e7e19eab5","name":"","group":"1add6f18.191f41","order":0,"width":0,"height":0,"passthru":false,"label":"Start","tooltip":"","color":"","bgcolor":"","icon":"","payload":"","payloadType":"str","topic":"topic","topicType":"msg","x":370,"y":300,"wires":[["f3974aa91ca73ccc"]]},{"id":"76f2281b369ec8b3","type":"ui_button","z":"ef43236e7e19eab5","name":"","group":"58ab9f631d25d819","order":0,"width":0,"height":0,"passthru":false,"label":"Start","tooltip":"","color":"","bgcolor":"","icon":"","payload":"","payloadType":"str","topic":"topic","topicType":"msg","x":370,"y":380,"wires":[["7c1a4134b2d3a215"]]},{"id":"0f543f3af487dbc2","type":"ui_group","name":"1st Video","tab":"bff636ce.5bde08","order":2,"disp":true,"width":8,"collapse":false},{"id":"1add6f18.191f41","type":"ui_group","name":"2nd Video","tab":"bff636ce.5bde08","order":3,"disp":true,"width":8,"collapse":false},{"id":"0436fb6b71c7e33a","type":"ui_group","name":"3rd Video","tab":"bff636ce.5bde08","order":3,"disp":true,"width":8,"collapse":false},{"id":"58ab9f631d25d819","type":"ui_group","name":"4th Video","tab":"bff636ce.5bde08","order":4,"disp":true,"width":8,"collapse":false},{"id":"bff636ce.5bde08","type":"ui_tab","name":"Movie link","icon":"dashboard","order":2,"disabled":false,"hidden":false}]