In Flexitive, you can set MP4 videos and YouTube videos to 'AutoPlay'.

Switching an MP4 video, or a YouTube video's AutoPlay toggle to ON will make the video start playing as soon as the video becomes visible on the canvas. 

If your design has a video set to AutoPlay, and the design is being viewed on an Android/iOS smartphone or tablet, you need to ensure your video sound is set to Mute. Autoplay on mobile is only allowed with muted sound. When the design is displayed, a mute button will appear. If someone viewing the design taps the mute button, the video will begin playing sound.