If you want to use transitions between slides where each slide has video background, there is a simple trick that will make it work. Have a look at this example – there is a nice horizontal sliding effect between slides. The trick is that these aren’t videos sliding, but background images taken from these videos (normally it will be a screenshot of the first video frame) instead. This means that you will need to set a background image for the slide, and the next – crucial – step is to add some delay before the video starts playing. This is where you do it:
How much delay should you set? This will depend on transition duration set for the particular slide, but if you leave 300 for transition duration (which is default), anything within 1000-1500 range will work. This is up to your personal preference on how you want the final result to look like.