Playing video’s during a webcast presentation may not always work due to limitations in the streaming capacity / internet bandwidth that you may have. This could cause your audience not seeing a fluent video but more like a slide show with some pictures, dropping frames, parts of the sound missing.
Hence, it would be a very disappointing experience for your audience and it doesn’t look very professional. Also it is a waste of your time as producing a video takes usually quite some time and this would be wasted if your audience can’t see the video properly. To overcome this you can upload the video for example to YouTube and make it a private video. During your webcast, you can provide a (redirected) link to the video and ask your audience to have a look at it. You can time it to ensure everyone starts watching the video at the same time and you can resume your webcast presentation after your audience had a chance to what the video.