In order to properly play a video in Zoom, you first want to click on the Share Screen button at the bottom navigation area. Next either select the video application that you want to share (e.g. Quicktime, Media Player, VLC, etc.), or the screen where you will show the video. Finally, at the bottom tray of the window make sure to select the option "Optimize Screen Sharing for Video Clip". Selecting this option will also enable "Share computer audio", which is also important.

Step by step on-screen of how to play a video in Zoom

When you play your video, it will broadcast at a good framerate and with good audio. When you are finished, simply select the red "Stop Share" button on the menu.

Stop Share location on menu