Play a video across multiple slides in PPT 2019

Go to the slide where you want the video to begin playing. Insert the video clip by going to Insert, Video, Video on my PC.

Select the video clip, under Video Tools click the Playback tab. In the Video Options group click the drop-down list next to Start and select Automatically.

Now click on the Animations tab, and choose the Animation pane button. In the animation pane double click the play entry.

In the dialog Play video, under stop playing activate the radio button After and enter the number of slides the video should play or put the maximum 999 so that the video will not stop. Finally click OK.

Be aware that the video will always play on top of the slide.