hello every one , i don't know my way is right or not but after done some try i found way using additive scene and play video on camera plane near , if anyone want to know comment i will share my code.
Step : 1
>> Create Empty Scene for play Fullscreen Video
>>In Empty Object take Video Player and Audio Source
>> set Render Mode Camera near plane and set camera
>> Aspect Ratio Fit Inside
Step : 2
>> Create script and add in same scene
>> Setup your video player like url set , and play pause , audio source set etc use for reference my script
https://drive.google.com/open?id=1BjwruJ5XRfLEsdMBgRolxoTEMCjOS_3G
Step 3 : On target Detect Load Fullscreen video play scene with additive For Example
SceneManager.LoadSceneAsync ("VideoPlayer", LoadSceneMode.Additive);
All done video play in full screen