On iOS I can simply remove the play button by doing
video::-webkit-media-controls-start-playback-button {
display: none !important;
}
How
For anyone who comes across this question, an alternative solution to the native one is to simply not include android-webview-video-poster:
in your Content Security Policy. This will block the image from ever loading in the first place. Not sure if this is considered a hackish solution, but it seems to work for me.