To play a video with sound on iOS, you need to capture a user gesture (such as a tap) before playing the video. You can either add a play button on the video which calls play() on the video when clicked (see our image target video with sound sample project), or you can add a splash screen which has the user tap the screen to start the experience (see our splash screen sample project).
How do I play alphaVideo after splash screen?
@tech_tech This might be a helpful thread:
Hope this helps 